PD-L1 binding fibronectin type III domains

ABSTRACT

FN3 domains that specifically bind to PD-L1, their conjugates, isolated nucleotides encoding the molecules, vectors, host cells, and methods of making and using them are useful in therapeutic and diagnostic applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser. No. 62/434,054, filed 14 Dec. 2016, the entire contents of which are incorporated herein by reference.

SEQUENCE LISTING

This application contains a Sequence Listing submitted via EFS-Web, the entire content of which is incorporated herein by reference. The ASCII text file, created on 11 Dec. 2017, is named JBI5113USNP_ST25.txt and is 124 kilobytes in size.

FIELD OF THE INVENTION

The present invention relates to fibronectin type III domains that specifically bind to PD-L1 and methods of making and using the molecules.

BACKGROUND OF THE INVENTION

The immune system is tightly controlled by a network of costimulatory and co-inhibitory ligands and receptors. These molecules provide secondary signals for T cell activation and provide a balanced network of positive and negative signals to maximize immune responses against infection and tumors, while limiting immunity to self (Wang et al., (Epub Mar. 7, 2011) J Exp Med 208(3):577-92; Lepenies et al., (2008) Endocr Metab Immune Disord Drug Targets 8:279-288).

Programmed Death-1 (PD-1) is a key immune checkpoint receptor expressed by activated T and B cells and mediates immunosuppression. The ligand for PD-1, PD-L1, is expressed by antigen-presenting cells and many cancers such as lung, ovarian and colon carcinoma and various myelomas. Binding of PD-L1 to PD-1 on T cells downregulates T cell proliferation and activation and drives T cell anergy and exhaustion in the tumor microenvironment, facilitating tumor cell escape from T-cell mediated immune surveillance.

Therapeutic efficacy of PD-1 and PD-L1 antagonists has been validated in clinical trials. However, response rates remain low. For example, Opdivo® (Nivolumab) treatment achieved a 26% objective response rate (ORR) across the 27 clinical trials analyzed (Tie et al., Int J Cancer 2016 Nov 4 doi: 10.1002/ijc.30501. [Epub ahead of print])

Measuring the expression of PD-L1 protein in the tumor tissue may aid in the early detection of cancer pathologies and may help assess the efficacy and durability of PD-L1 and PD-1 antagonists. For example, PD-L1 expression in at least 50% of tumor cells correlated with improved efficacy of Keytruda® (pembrolizumab) (Garon et al., N Engl J Med 2015; 372:2018-2028), and PD-L1 expression has been correlated with poor prognosis (see for example Wang et al., Eur J Surg oncol 2015 Apr; 41(4):450-6).

However, the use of PD-L1 protein expression as an accurate predictor for cancer and/or the efficacy of anti-PD-1 and anti-PD-L1 directed therapies remain challenging partially due to observed variability in results depending on the detection reagent used. For example, the evaluation of PD-L1 expression in non-small cell lung cancer samples using commercially available assays such as PD-L1 (E1L3NO) XP® Rabbit mAb (Cell Signaling) and Ventana PD-L1 (SP142) Assay yielded discordant results (McLaughlin et al., JAMA Oncol 2016 Jan;2(1):46-54)

Therefore, there is a need for reagents to accurately detect PD-L1 in tumor tissues and other samples and new therapeutics that modulate the interaction between PD-L1 and PD-1.

SUMMARY OF THE INVENTION

The invention provides an isolated FN3 domain that specifically binds to PD-L1.

The invention also provides an isolated FN3 domain that specifically binds to PD-L1 comprising the sequence of SEQ ID NOs: 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123 or 124.

The invention also provides an isolated polynucleotide encoding the FN3 domain that specifically binds to PD-L1 of the invention.

The invention also provides a vector comprising the polynucleotide of the invention.

The invention also provides a host cell comprising the vector of the invention.

The invention also provides a method of producing the FN3 domain that specifically binds to PD-L1 of the invention, comprising culturing the isolated host cell of the invention under conditions that the FN3 domain that specifically binds to PD-L1 is expressed, and purifying the FN3 domain that specifically binds to PD-L1.

The invention also provides a pharmaceutical composition comprising the FN3 domain that specifically binds to PD-L1 of the invention and a pharmaceutically acceptable carrier.

The invention also provides an anti-idiotypic antibody that specifically binds the FN3 domain that specifically binds to PD-L1 of the invention.

The invention also provides a kit comprising the FN3 domain of the invention.

The invention also provides a method of detecting PD-L1-expressing cancer cells in a tumor tissue, comprising

-   -   obtaining a sample of the tumor tissue from a subject; and     -   detecting whether PD-L1 is expressed in the tumor tissue by         contacting the sample of the tumor tissue with the FN3 domain         that specifically binds to PD-L1 comprising the sequence of any         one of SEQ ID NOs: 34-124 and detecting the binding between         PD-L1 and the FN3 domain.

The invention also provides a method of isolating or detecting PD-L1 expressing cells, comprising obtaining a sample from a subject;

-   -   contacting the sample with the FN3 domain that specifically         binds to PD-L1     -   comprising the sequence of any one of SEQ ID NOs: 34-124, and     -   isolating or detecting the cells bound to the FN3 domains.

The invention also provides a method of detecting PD-L1-expressing cancer cells in a tumor tissue, comprising

-   -   conjugating the FN3 domain that specifically binds to PD-L1         comprising the sequence of any one of SEQ ID NOs: 34-124 to a         detectable label to form a conjugate;     -   administering the conjugate to a subject; and     -   visualizing the PD-L1 expressing cancer cells to which the         conjugate is bound.

DETAILED DESCRIPTION OF THE INVENTION

As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to “a cell” includes a combination of two or more cells, and the like.

“Fibronectin type III (FN3) domain” (FN3 domain) refers to a domain occurring frequently in proteins including fibronectins, tenascin, intracellular cytoskeletal proteins, cytokine receptors and prokaryotic enzymes (Bork and Doolittle, Proc Nat Acad Sci USA 89:8990-8994, 1992; Meinke et al., J Bacteriol 175:1910-1918, 1993; Watanabe et al., J Biol Chem 265:15659-15665, 1990). Exemplary FN3 domains are the 15 different FN3 domains present in human tenascin C, the 15 different FN3 domains present in human fibronectin (FN), and non-natural synthetic FN3 domains as described for example in U.S. Pat. No. 8,278,419. Individual FN3 domains are referred to by domain number and protein name, e.g., the 3^(rd) FN3 domain of tenascin (TN3), or the 10^(th) FN3 domain of fibronectin (FN10).

“Centyrin” refers to a FN3 domain that is based on the consensus sequence of the 15 different FN3 domains present in human tenascin C.

The term “capture agent” refers to substances that bind to a particular type of cells and enable the isolation of that cell from other cells. Exemplary capture agents are magnetic beads, ferrofluids, encapsulating reagents, molecules that bind the particular cell type and the like.

“Sample” refers to a collection of similar fluids, cells, or tissues isolated from a subject, as well as fluids, cells, or tissues present within a subject. Exemplary samples are tissue biopsies, fine needle aspirations, surgically resected tissue, organ cultures, cell cultures and biological fluids such as blood, serum and serosal fluids, plasma, lymph, urine, saliva, cystic fluid, tear drops, feces, sputum, mucosal secretions of the secretory tissues and organs, vaginal secretions, ascites fluids, fluids of the pleural, pericardial, peritoneal, abdominal and other body cavities, fluids collected by bronchial lavage, synovial fluid, liquid solutions contacted with a subject or biological source, for example, cell and organ culture medium including cell or organ conditioned medium and lavage fluids and the like.

“Substituting” or “substituted” or “mutating” or “mutated” refers to altering, deleting of inserting one or more amino acids or nucleotides in a polypeptide or polynucleotide sequence to generate a variant of that sequence.

“Variant” refers to a polypeptide or a polynucleotide that differs from a reference polypeptide or a reference polynucleotide by one or more modifications for example, substitutions, insertions or deletions.

“Specifically binds” or “specific binding” refers to the ability of the FN3 domain of the invention to bind PD-L1 with a dissociation constant (K_(D)) of about 1×10⁻⁶ M or less, for example about 1×10⁻⁷ M or less, about 1×10⁻⁸ M or less, about 1×10⁻⁹ M or less, about 1×10⁻¹⁰ M or less, about 1×10⁻¹¹ M or less, about 1×10⁻¹² M or less, or about 1×10⁻¹³ M or less. Alternatively, “specific binding” refers to the ability of the FN3 domain of the invention to bind PD-L1 at least 5-fold above the negative control in standard ELISA assay. The isolated FN3 domain of the invention that specifically binds PD-L1 may, however, have cross-reactivity to other related antigens, for example to the same predetermined antigen from other species (homologs), such as Macaca Fascicularis (cynomolgous monkey, cyno) or Pan troglodytes (chimpanzee).

“Library” refers to a collection of variants. The library may be composed of polypeptide or polynucleotide variants.

“Stability” refers to the ability of a molecule to maintain a folded state under physiological conditions such that it retains at least one of its normal functional activities, for example, binding to a predetermined antigen such as PD-L1.

“PD-L1” refers to human PD-L1 protein having the amino acid sequence of SEQ ID NO: 32. The extracellular domain of PD-L1 spans residues 1-220, the transmembrane domain spans residues 221-241 and the cytoplasmic domain spans residues 242-272.

“PD-1” refers to human PD-1 protein having the amino acid sequence of SEQ ID NO: 33. The extracellular domain of PD-1 spans residues 1-150, the transmembrane domain spans residues 151-171 and the cytoplasmic domain spans residues 172-268 of SEQ ID NO: 33.

“Tencon” refers to the synthetic fibronectin type III (FN3) domain having the sequence shown in SEQ ID NO: 1 and described in U.S. Pat. Publ. No. 2010/0216708.

A “cancer cell” or a “tumor cell” refers to a cancerous, pre-cancerous or transformed cell, either in vivo, ex vivo, and in tissue culture, that has spontaneous or induced phenotypic changes that do not necessarily involve the uptake of new genetic material. Although transformation can arise from infection with a transforming virus and incorporation of new genomic nucleic acid, or uptake of exogenous nucleic acid, it can also arise spontaneously or following exposure to a carcinogen, thereby mutating an endogenous gene. Transformation/cancer is exemplified by, e.g., morphological changes, immortalization of cells, aberrant growth control, foci formation, proliferation, malignancy, tumor specific markers levels, invasiveness, tumor growth or suppression in suitable animal hosts such as nude mice, and the like, in vitro, in vivo, and ex vivo (Freshney, Culture of Animal Cells: A Manual of Basic Technique (3rd ed. 1994)).

“Vector” refers to a polynucleotide capable of being duplicated within a biological system or that can be moved between such systems. Vector polynucleotides typically contain elements, such as origins of replication, polyadenylation signal or selection markers that function to facilitate the duplication or maintenance of these polynucleotides in a biological system. Examples of such biological systems may include a cell, virus, animal, plant, and reconstituted biological systems utilizing biological components capable of duplicating a vector. The polynucleotide comprising a vector may be DNA or RNA molecules or a hybrid of these.

“Expression vector” refers to a vector that can be utilized in a biological system or in a reconstituted biological system to direct the translation of a polypeptide encoded by a polynucleotide sequence present in the expression vector.

“Polynucleotide” refers to a synthetic molecule comprising a chain of nucleotides covalently linked by a sugar-phosphate backbone or other equivalent covalent chemistry. cDNA is a typical example of a polynucleotide.

“Polypeptide” or “protein” refers to a molecule that comprises at least two amino acid residues linked by a peptide bond to form a polypeptide. Small polypeptides of less than about 50 amino acids may be referred to as “peptides”.

“Valent” refers to the presence of a specified number of binding sites specific for an antigen in a molecule. As such, the terms “monovalent”, “bivalent”, “tetravalent”, and “hexavalent” refer to the presence of one, two, four and six binding sites, respectively, specific for an antigen in a molecule.

“Subject” includes any human or nonhuman animal “Nonhuman animal” includes all vertebrates, e.g., mammals and non-mammals, such as nonhuman primates, sheep, dogs, cats, horses, cows chickens, amphibians, reptiles, etc. Except when noted, the terms “patient” or “subject” are used interchangeably.

“Isolated” refers to a homogenous population of molecules (such as synthetic polynucleotides or a polypeptide such as FN3 domains) which have been substantially separated and/or purified away from other components of the system the molecules are produced in, such as a recombinant cell, as well as a protein that has been subjected to at least one purification or isolation step. “Isolated FN3 domain” refers to an FN3 domain that is substantially free of other cellular material and/or chemicals and encompasses FN3 domains that are isolated to a higher purity, such as to 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% purity.

Compositions of Matter

The present invention provides fibronectin type III (FN3) domains that specifically bind PD-L1. These molecules can be used in therapeutic and diagnostic applications and in imaging. The present invention provides polynucleotides encoding the FN3 domains of the invention or complementary nucleic acids thereof, vectors, host cells, and methods of making and using them.

The invention provides an isolated FN3 domain that specifically binds PD-L1.

The FN3 domain of the invention may bind PD-L1 with a dissociation constant (K_(D)) of less than about 1×10⁻⁷ M, for example less than about 1×10⁻⁸ M, less than about 1×10⁻⁹ M, less than about 1×10⁻¹° M, less than about 1×10⁻¹¹ M, less than about 1×10⁻¹² M, or less than about 1×10⁻¹³ M as determined by surface plasmon resonance or the Kinexa method, as practiced by those of skill in the art. The measured affinity of a particular FN3 domain-antigen interaction can vary if measured under different conditions (e.g., osmolarity, pH). Thus, measurements of affinity and other antigen-binding parameters (e.g., K_(D), K_(on), K_(off)) are made with standardized solutions of protein scaffold and antigen, and a standardized buffer, such as the buffer described herein.

The FN3 domain of the invention may bind PD-L1 at least 5-fold above the signal obtained for a negative control in standard ELISA assay.

In some embodiments, the FN3 domain that specifically binds PD-L1 comprises an initiator methionine (Met) linked to the N-terminus of the molecule.

In some embodiments, the FN3 domain that specifically binds PD-L1 comprises a cysteine (Cys) linked to a C-terminus of the FN3 domain.

The addition of the N-terminal Met and/or the C-terminal Cys may facilitate expression and/or conjugation of half-life extending molecules.

In some embodiments, the FN3 domain that specifically binds PD-L1 is internalized into a cell.

Internalization of the FN3 domain may facilitate delivery of a cytotoxic agent into tumor cells.

In some embodiments, the FN3 domain that specifically binds PD-L1 inhibits binding of PD-L1 to PD-1.

Inhibition of binding of PD-L1 to PD-1 by the FN3 domains of the invention may be assessed using competition ELISA. In an exemplary assay, 1 μg/ml recombinant human PD-L1 extracellular domain is bound on wells of microtiter plates, the wells are washed and blocked, and 10 μg/ml of the test FN3 domain is added. Without washing, 7.5 μg/ml PD-1 extracellular domain is added into the wells and incubated for 30 min, after which 0.5 μg/ml anti-PD-1 antibody is added and incubated for 30 min. The plates are washed and 0.5 μg/mL neutravidin-HRP conjugate polyclonal antibody is added and incubated for 30 minutes. The plates are washed and POD Chemiluminescence substrate added immediately prior to reading the luminescence signal. The FN3 domains of the invention inhibit binding of PD-L1 to PD-1 when the binding of PD-1 is reduced by at least about 80%, 85%, 90%, 95% or 100%.

In some embodiments, the FN3 domain that specifically binds PD-L1 is a PD-L1 antagonist.

In some embodiments, the FN3 domain that specifically binds PD-L1 is a PD-L1 agonist.

“Antagonist” refers to a FN3 domain that specifically binds PD-L1 that suppresses at least one reaction or activity that is induced by PD-L1 binding PD-1. A molecule is an antagonist when the at least one reaction or activity is suppressed by at least about 30%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% more than the at least one reaction or activity suppressed in the absence of the antagonist (e.g., negative control), or when the suppression is statistically significant when compared to the suppression in the absence of the antagonist. A typical reaction or activity that is induced by PD-L1 binding PD-1 is reduced antigen-specific CD4⁺ or CD8⁺ cell proliferation or reduced interferon-γ (IFN-γ) production by T cells.

The antagonistic FN3 domains that specifically bind PD-L1 may be used in the treatment of cancer or viral infections and in general in treatment of diseases in which activation of immune responses is desirable.

“Agonist” refers to a FN3 domain that specifically binds PD-L1 that induces at least one reaction or activity that is induced by PD-L1 binding PD-1. The FN3 domain is an agonist when the at least one reaction or activity is induced by at least about 30%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% greater than the at least one reaction or activity induced in the absence of the agonist (e.g., negative control), or when the induction is statistically significant when compared to the induction in the absence of the agonist. A typical reaction or activity that is induced by PD-L1 binding PD-1 is reduced antigen-specific CD4⁺ or CD8⁺ cell proliferation or reduced interferon-γ (IFN-γ) production by T cells.

The agonistic FN3 domains that specifically bind PD-L1 may be used in the treatment of autoimmune or inflammatory diseases and in general diseases in which suppression of immune responses is desirable.

In some embodiments, the FN3 domain that specifically binds PD-L1 does not inhibit binding of PD-L1 to PD-1.

In some embodiments, the FN3 domain that specifically binds PD-L1 does not activate signaling downstream of PD-1.

In some embodiments, the FN3 domain that specifically binds PD-L1 is based on Tencon sequence of SEQ ID NO: 1 or Tencon 27 sequence of SEQ ID NO: 4, optionally having substitutions at residues positions 11, 14, 17, 37, 46, 73, and/or 86 (residue numbering corresponding to SEQ ID NO: 4).

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NOs: 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123 and/or 124.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 34.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 35.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 36.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 37.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 38.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 39.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 40.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 41.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 42.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 43.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 44.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 45.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 46.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 47.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 48.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 49.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 50.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 51.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 52.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 53.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 54.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 55.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 56.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 57.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 58.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 59.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 60.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 61.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 62.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 63.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 64.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 65.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 66.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 67.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 68.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 69.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 70.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 71.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 72.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 73.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 74.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 75.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 76.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 77.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 78.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 79.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 80.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 81.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 82.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 83.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 84.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 85.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 86.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 87.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 88.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 89.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 90.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 91.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 92.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 93.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 94.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 95.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 96.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 97.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 98.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 99.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 100.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 101.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 102.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 103.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 104.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 105.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 106.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 107.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 108.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 109.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 110.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 111.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 112.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 113.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 114.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 115.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 116.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 117.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 118.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 119.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 120.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 121.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 122.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 123.

The invention also provides an isolated FN3 domain that specifically binds PD-L1 comprising the amino acid sequence of SEQ ID NO: 124.

In some embodiments, the isolated FN3 domain that specifically binds PD-L1 comprises an initiator methionine (Met) linked to the N-terminus of the molecule.

in some embodiments, the isolated FN3 domain that specifically binds PD-L1 comprises an amino acid sequence that is 62%, 63%, 64% , 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% identical to the amino acid sequence of SEQ ID NO: 74.

In some embodiments, the isolated FN3 domain that specifically binds PD-L1 comprises an amino acid sequence that is 62%, 63%, 64% , 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% identical to the amino acid sequence of any one of SEQ ID NOs: 34-124.

Conjugates of the FN3 Domains that Specifically Bind PD-L1 of the Invention

The invention also provides an isolated FN3 domain that specifically binds PD-L1 conjugated to a heterologous molecule(s).

In some embodiments, the heterologous molecule is a detectable label or a cytotoxic agent.

The invention also provides an FN3 domain that specifically binds PD-L1 conjugated to a detectable label.

The invention also provides an FN3 domain that specifically binds PD-L1 conjugated to a cytotoxic agent.

In some embodiments, the detectable label is also a cytotoxic agent.

The FN3 domains that specifically bind PD-L1 of the invention conjugated to a detectable label can be used to evaluate expression of PD-L1 on samples such as tumor tissue in vivo or in vitro.

Detectable label includes compositions that when conjugated to the FN3 domains that specifically bind PD-L 1 of the invention renders the latter detectable, via spectroscopic, photochemical, biochemical, immunochemical, or chemical means.

Exemplary detectable labels include radioactive isotopes, magnetic beads, metallic beads, colloidal particles, fluorescent dyes, electron-dense reagents, enzymes (for example, as commonly used in an ELISA), biotin, digoxigenin, haptens, luminescent molecules, chemiluminescent molecules, fluorochromes, fluorophores, fluorescent quenching agents, colored molecules, radioactive isotopes, scintillants, avidin, streptavidin, protein A, protein G, antibodies or fragments thereof, poly histidine, Ni2+, Flag tags, myc tags, heavy metals, enzymes, alkaline phosphatase, peroxidase, luciferase, electron donors/acceptors, acridinium esters, and colorimetric substrates.

A detectable label may emit a signal spontaneously, such as when the detectable label is a radioactive isotope. In other cases the detectable label emits a signal as a result of being stimulated by an external field.

Exemplary radioactive isotopes may be y-emitting, Auger-emitting, β-emitting, an alpha-emitting or positron-emitting radioactive isotope. Exemplary radioactive isotopes include ³H, ¹¹C, ¹³C, ¹⁵N, ¹⁸F, ¹⁹F, ⁵⁵Co, ⁵⁷Co, ⁶⁰Co, ⁶¹Cu, ⁶²Cu, ⁶⁴Cu, ⁶⁷Cu, ⁶⁸Cu, ⁷²As, ⁷⁵Br, ⁸⁶Y, ⁸⁹Zr, ⁹⁰Sr, ^(94m)Tc, ^(99m)Tc, ¹¹⁵In, ¹²³I, ¹²⁴I, ¹²⁵I, ¹³¹I, ²¹¹At, ²¹²Bi, ²¹³Bi, ²²³Ra, ²²⁶Ra, ²²⁵Ac and ²²⁷Ac.

Exemplary metal atoms are metals with an atomic number greater than 20, such as calcium atoms, scandium atoms, titanium atoms, vanadium atoms, chromium atoms, manganese atoms, iron atoms, cobalt atoms, nickel atoms, copper atoms, zinc atoms, gallium atoms, germanium atoms, arsenic atoms, selenium atoms, bromine atoms, krypton atoms, rubidium atoms, strontium atoms, yttrium atoms, zirconium atoms, niobium atoms, molybdenum atoms, technetium atoms, ruthenium atoms, rhodium atoms, palladium atoms, silver atoms, cadmium atoms, indium atoms, tin atoms, antimony atoms, tellurium atoms, iodine atoms, xenon atoms, cesium atoms, barium atoms, lanthanum atoms, hafnium atoms, tantalum atoms, tungsten atoms, rhenium atoms, osmium atoms, iridium atoms, platinum atoms, gold atoms, mercury atoms, thallium atoms, lead atoms, bismuth atoms, francium atoms, radium atoms, actinium atoms, cerium atoms, praseodymium atoms, neodymium atoms, promethium atoms, samarium atoms, europium atoms, gadolinium atoms, terbium atoms, dysprosium atoms, holmium atoms, erbium atoms, thulium atoms, ytterbium atoms, lutetium atoms, thorium atoms, protactinium atoms, uranium atoms, neptunium atoms, plutonium atoms, americium atoms, curium atoms, berkelium atoms, californium atoms, einsteinium atoms, fermium atoms, mendelevium atoms, nobelium atoms, or lawrencium atoms.

In some embodiments, the metal atoms may be alkaline earth metals with an atomic number greater than twenty.

In some embodiments, the metal atoms may be lanthanides.

In some embodiments, the metal atoms may be actinides.

In some embodiments, the metal atoms may be transition metals.

In some embodiments, the metal atoms may be poor metals.

In some embodiments, the metal atoms may be gold atoms, bismuth atoms, tantalum atoms, and gadolinium atoms.

In some embodiments, the metal atoms may be metals with an atomic number of 53 (i.e. iodine) to 83 (i.e. bismuth).

In some embodiments, the metal atoms may be atoms suitable for magnetic resonance imaging.

The metal atoms may be metal ions in the form of +1 , +2, or +3 oxidation states, such as Ba²⁺, Bi³⁺, Cs⁺, Ca²⁺, Cr²⁺, Cr³⁺, Cr⁶⁺, Co³⁺, Co³⁺, Cu⁺, Cu²⁺, Cu³⁺, Ga³⁺, Gd³⁺, Au⁺, Au³⁺, Pe²⁺, Fe³⁺, F³⁺, Pb²⁺, Mn²⁺, Mn³⁺, Mn⁴⁺, Mn⁷⁺, Hg²⁺, Ni²⁺, Ni³⁺, Ag⁺, Sr²⁺, Sn²⁺, Sn⁴⁺, and Zn²⁺. The metal atoms may comprise a metal oxide, such as iron oxide, manganese oxide, or gadolinium oxide.

Suitable dyes include any commercially available dyes such as, for example, 5(6)-carboxyfluorescein, IRDye 680RD maleimide or IRDye 800CW, ruthenium polypyridyl dyes, and the like.

Suitable fluorophores are fluorescein isothiocyante (FITC), fluorescein thiosemicarbazide, rhodamine, Texas Red, CyDyes (e.g., Cy3, Cy5, Cy5.5), Alexa Fluors (e.g., Alexa488, Alexa555, Alexa594; Alexa647), near infrared (NIR) (700-900 nm) fluorescent dyes, and carbocyanine and aminostyryl dyes.

The FN3 domains that specifically bind PD-L1 conjugated to a detectable label may be used as an imaging agent to evaluate tumor distribution, diagnosis for the presence of tumor cells and/or, recurrence of tumor.

In some embodiments, the FN3 domains that specifically bind PD-L1 of the invention are conjugated to a cytotoxic agent.

In some embodiments, the cytotoxic agent is a chemotherapeutic agent, a drug, a growth inhibitory agent, a toxin (e.g., an enzymatically active toxin of bacterial, fungal, plant, or animal origin, or fragments thereof), or a radioactive isotope (i.e., a radioconjugate).

The FN3 domains that specifically bind PD-L1 conjugated to a cytotoxic agent of the invention may be used in the targeted delivery of the cytotoxic agent to PD-L1 expressing tumor cell, and intracellular accumulation therein, wherein systemic administration of these unconjugated cytotoxic agents may result in unacceptable levels of toxicity to normal cells.

In some embodiments, the cytotoxic agent is daunomycin, doxorubicin, methotrexate, vindesine, bacterial toxins such as diphtheria toxin, ricin, geldanamycin, maytansinoids or calicheamicin. The cytotoxic agent may elict their cytotoxic and cytostatic effects by mechanisms including tubulin binding, DNA binding, or topoisomerase inhibition.

In some embodiments, the cytotoxic agent is an enzymatically active toxins such as diphtheria A chain, nonbinding active fragments of diphtheria toxin, exotoxin A chain (from Pseudomonas aeruginosa), ricin A chain, abrin A chain, modeccin A chain, alpha-sarcin, Aleurites fordii proteins, dianthin proteins, Phytolaca americana proteins (PAPI, PAPII, and PAP-S), momordica charantia inhibitor, curcin, crotin, sapaonaria officinalis inhibitor, gelonin, mitogellin, restrictocin, phenomycin, enomycin, and the tricothecenes.

In some embodiments, the cytotoxic agent is a radionuclide, such as ²¹²Bi, ¹³¹I, ¹³¹In, ⁹⁰Y, and ¹⁸⁶Re.

In some embodiments, the cytotoxic agent is dolastatins or dolostatin peptidic analogs and derivatives, auristatin or monomethyl auristatin phenylalanine Exemplary molecules are disclosed in U.S. Pat Nos. 5,635,483 and 5,780,588. Dolastatins and auristatins have been shown to interfere with microtubule dynamics, GTP hydrolysis, and nuclear and cellular division (Woyke et al (2001) Antimicrob Agents and Chemother. 45(12):3580-3584) and have anticancerand antifungal activity. The dolastatin or auristatin drug moiety may be attached to the FN3 domain of the invention through the N (amino) terminus or the C (carboxyl) terminus of the peptidic drug moiety (WO 02/088172), or via any cysteine engineered into the FN3 domain.

The FN3 domains that specifically bind PD-L1 of the invention may be conjugated to a detectable label using known methods.

In some embodiments, the detectable label is complexed with a chelating agent.

In some embodiments, the detectable label is conjugated to the FN3 domain that specifically binds PD-L1 of the invention via a linker.

The detectable label or the cytotoxic moiety may be linked directly, or indirectly, to the FN3 domain that specifically binds PD-L1 of the invention using known methods. Suitable linkers are known in the art and include, for example, prosthetic groups, non-phenolic linkers (derivatives of N-succimidyl-benzoates; dodecaborate), chelating moieties of both macrocyclics and acyclic chelators, such as derivatives of 1,4,7,10-tetraazacyclododecane-1,4,7,10,tetraacetic acid (DOTA), derivatives of diethylenetriaminepentaacetic avid (DTPA), derivatives of S-2-(4-Isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) and derivatives of 1,4,8,11-tetraazacy clodocedan-1,4,8,11-tetraacetic acid (TETA), N-succinimidyl-3 -(2-pyridyldithiol) propionate (SPDP), iminothiolane (IT), bifunctional derivatives of imidoesters (such as dimethyl adipimidate HC1), active esters (such as disuccinimidyl suberate), aldehydes (such as glutaraldehyde), bis-azido compounds (such as bis(p-azidobenzoyl)hexanediamine), bis-diazonium derivatives (such as bis-(p-diazoniumbenzoyl)-ethylenediamine), diisocyanates (such as toluene 2,6-diisocyanate), and bis-active fluorine compounds (such as 1,5-difluoro-2,4-dinitrobenzene) and other chelating moieties. Suitable peptide linkers are well known.

In some embodiment, the FN3 domain that specifically binds PD-L1 is removed from the blood via renal clearance.

Isolation of PD-L1 binding FN3 domains from a library based on Tencon sequence

Tencon (SEQ ID NO: 1) is a non-naturally occurring fibronectin type III (FN3) domain designed from a consensus sequence of fifteen FN3 domains from human tenascin-C (Jacobs et al., Protein Engineering, Design, and Selection, 25:107-117, 2012; U.S. Pat. Publ. No. 2010/0216708). The crystal structure of Tencon shows six surface-exposed loops that connect seven beta-strands as is characteristic to the FN3 domains, the beta-strands referred to as A, B, C, D, E, F, and G, and the loops referred to as AB, BC, CD, DE, EF, and FG loops (Bork and Doolittle, Proc Natl Acad Sci USA 89:8990-8992, 1992; U.S. Pat. No. 6,673,901). These loops, or selected residues within each loop, may be randomized in order to construct libraries of fibronectin type III (FN3) domains that may be used to select novel molecules that bind Pd-L1. Table 1 shows positions and sequences of each loop and beta-strand in Tencon (SEQ ID NO: 1).

Library designed based on Tencon sequence may thus have randomized FG loop, or randomized BC and FG loops, such as libraries TCL1 or TCL2 as described below. The Tencon BC loop is 7 amino acids long, thus 1, 2, 3, 4, 5, 6 or 7 amino acids may be randomized in the library diversified at the BC loop and designed based on Tencon sequence. The Tencon FG loop is 7 amino acids long, thus 1, 2, 3, 4, 5, 6 or 7 amino acids may be randomized in the library diversified at the FG loop and designed based on Tencon sequence. Further diversity at loops in the Tencon libraries may be achieved by insertion and/or deletions of residues at loops. For example, the FG and/or BC loops may be extended by 1-22 amino acids, or decreased by 1-3 amino acids. The FG loop in Tencon is 7 amino acids long, whereas the corresponding loop in antibody heavy chains ranges from 4-28 residues. To provide maximum diversity, the FG loop may be diversified in sequence as well as in length to correspond to the antibody CDR3 length range of 4-28 residues. For example, the FG loop can further be diversified in length by extending the loop by additional 1, 2, 3, 4 or 5 amino acids.

Library designed based on Tencon sequence may also have randomized alternative surfaces that form on a side of the FN3 domain and comprise two or more beta strands, and at least one loop. One such alternative surface is formed by amino acids in the C and the F beta-strands and the CD and the FG loops (a C-CD-F-FG surface). A library design based on Tencon alternative C-CD-F-FG surface is described in U.S. Pat. Publ. No. US2013/0226834. Library designed based on Tencon sequence also includes libraries designed based on Tencon variants, such as Tencon variants having substitutions at residues positions 11, 14, 17, 37, 46, 73, or 86 (residue numbering corresponding to SEQ ID NO: 1), and which variants display improve thermal stability. Exemplary Tencon variants are described in US Pat. Publ. No. 2011/0274623, and include Tencon27 (SEQ ID NO: 4) having substitutions E 11R, L17A, N46V and E861 when compared to Tencon of SEQ ID NO: 1.

TABLE 1 Tencon FN3 domain (SEQ ID NO: 1) A strand  1-12 AB loop 13-16 B strand 17-21 BC loop 22-28 C strand 29-37 CD loop 38-43 D strand 44-50 DE loop 51-54 E strand 55-59 EF loop 60-64 F strand 65-74 FG loop 75-81 G strand 82-89

Tencon and other FN3 sequence based libraries may be randomized at chosen residue positions using a random or defined set of amino acids. For example, variants in the library having random substitutions may be generated using NNK codons, which encode all 20 naturally occurring amino acids. In other diversification schemes, DVK codons may be used to encode amino acids Ala, Trp, Tyr, Lys, Thr, Asn, Lys, Ser, Arg, Asp, Glu, Gly, and Cys. Alternatively, NNS codons may be used to give rise to all 20 amino acid residues and simultaneously reducing the frequency of stop codons. Libraries of FN3 domains with biased amino acid distribution at positions to be diversified may be synthesized for example using Slonomics® technology (http:_/www_sloning_com). This technology uses a library of pre-made double stranded triplets that act as universal building blocks sufficient for thousands of gene synthesis processes. The triplet library represents all possible sequence combinations necessary to build any desired DNA molecule. The codon designations are according to the well-known IUB code.

The FN3 domains that specifically bind PD-L1 of the invention may be isolated by producing the FN3 library such as the Tencon library using cis display to ligate DNA fragments encoding the scaffold proteins to a DNA fragment encoding RepA to generate a pool of protein-DNA complexes formed after in vitro translation wherein each protein is stably associated with the DNA that encodes it (U.S. Pat. No. 7,842,476; Odegrip et al., Proc Natl Acad Sci U S A 101, 2806-2810, 2004), and assaying the library for specific binding to PSMA by any method known in the art and described in the Example. Exemplary well known methods which can be used are ELISA, sandwich immunoassays, and competitive and non-competitive assays (see, e.g., Ausubel et al., eds, 1994, Current Protocols in Molecular Biology, Vol. 1, John Wiley & Sons, Inc., New York). The identified FN3 domains that specifically bind PD-L1 are further characterized for their binding to PD-L1, modulation of PD-L1 activity, internalization, stability, and other desired characteristics.

The FN3 domains that specifically bind PD-L1 of the invention may be generated using any FN3 domain as a template to generate a library and screening the library for molecules specifically binding PD-L1 using methods provided within. Exemplar FN3 domains that may be used are the 3rd FN3 domain of tenascin C (TN3) (SEQ ID NO: 125), Fibcon (SEQ ID NO: 126), and the 10^(th) FN3 domain of fibronectin (FN10) (SEQ ID NO: 127). Standard cloning and expression techniques are used to clone the libraries into a vector or synthesize double stranded cDNA cassettes of the library, to express, or to translate the libraries in vitro. For example ribosome display (Hanes and Pluckthun, Proc Natl Acad Sci USA, 94, 4937-4942, 1997), mRNA display (Roberts and Szostak, Proc Natl Acad Sci USA, 94, 12297-12302, 1997), or other cell-free systems (U.S. Pat. No. 5,643,768) can be used. The libraries of the FN3 domain variants may be expressed as fusion proteins displayed on the surface for example of any suitable bacteriophage. Methods for displaying fusion polypeptides on the surface of a bacteriophage are well known (U. S. Pat. Publ. No. 2011/0118144; Int. Pat. Publ. No. WO2009/085462; U.S. Pat. No. 6,969,108; U.S. Pat. No. 6,172,197; U.S. Pat. No. 5,223,409; U.S. Pat. No. 6,582,915; U.S. Pat. No. 6,472,147).

In some embodiments, the FN3 domain that specifically binds PD-L1 is based on Tencon sequence of SEQ ID NO: 1 or Tencon27 sequence of SEQ ID NO: 4, the SEQ ID NO: 1 or the SEQ ID NO: 4, optionally having substitutions at residues positions 11, 14, 17, 37, 46, 73, and/or 86.

The FN3 domains that specifically bind PD-L1 of the invention may be modified to improve their properties such as improve thermal stability and reversibility of thermal folding and unfolding. Several methods have been applied to increase the apparent thermal stability of proteins and enzymes, including rational design based on comparison to highly similar thermostable sequences, design of stabilizing disulfide bridges, mutations to increase alpha-helix propensity, engineering of salt bridges, alteration of the surface charge of the protein, directed evolution, and composition of consensus sequences (Lehmann and Wyss, Curr Opin Biotechnol, 12, 371-375, 2001). High thermal stability may increase the yield of the expressed protein, improve solubility or activity, decrease immunogenicity, and minimize the need of a cold chain in manufacturing. Residues that may be substituted to improve thermal stability of Tencon (SEQ ID NO: 1) are residue positions 11, 14, 17, 37, 46, 73, or 86, and are described in US Pat. Publ. No. 2011/0274623. Substitutions corresponding to these residues may be incorporated to the FN3 domain containing molecules of the invention.

Measurement of protein stability and protein lability can be viewed as the same or different aspects of protein integrity. Proteins are sensitive or “labile” to denaturation caused by heat, by ultraviolet or ionizing radiation, changes in the ambient osmolarity and pH if in liquid solution, mechanical shear force imposed by small pore-size filtration, ultraviolet radiation, ionizing radiation, such as by gamma irradiation, chemical or heat dehydration, or any other action or force that may cause protein structure disruption. The stability of the molecule can be determined using standard methods. For example, the stability of a molecule can be determined by measuring the thermal melting (“T_(m)”) temperature, the temperature in ° Celsius (° C.) at which half of the molecules become unfolded, using standard methods. Typically, the higher the T_(m), the more stable the molecule. In addition to heat, the chemical environment also changes the ability of the protein to maintain a particular three dimensional structure.

In one embodiment, the FN3 domain that specifically binds PD-L1 of the invention may exhibit increased stability by at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95% or more compared to the same domain prior to engineering measured by the increase in the T..

Chemical denaturation can likewise be measured by a variety of methods. Chemical denaturants include guanidinium hydrochloride, guanidinium thiocyanate, urea, acetone, organic solvents (DMF, benzene, acetonitrile), salts (ammonium sulfate, lithium bromide, lithium chloride, sodium bromide, calcium chloride, sodium chloride); reducing agents (e.g. dithiothreitol, beta-mercaptoethanol, dinitrothiobenzene, and hydrides, such as sodium borohydride), non-ionic and ionic detergents, acids (e.g. hydrochloric acid (HCl), acetic acid (CH₃COOH), halogenated acetic acids), hydrophobic molecules (e.g. phosopholipids), and targeted denaturants. Quantitation of the extent of denaturation can rely on loss of a functional property, such as ability to bind a target molecule, or by physiochemical properties, such as tendency to aggregation, exposure of formerly solvent inaccessible residues, or disruption or formation of disulfide bonds.

The FN3 domain that specifically binds PD-L1 of the invention may be generated as monomers, dimers, or multimers, for example, as a means to increase the valency and thus the avidity of target molecule binding, or to generate bi- or multispecific scaffolds simultaneously binding two or more different target molecules. The dimers and multimers may be generated by linking monospecific, bi- or multispecific protein scaffolds, for example, by the inclusion of an amino acid linker, for example a linker containing poly-glycine, glycine and serine, or alanine and proline. Exemplary linker include (GS)2, (SEQ ID NO: 128), (GGGS)2 (SEQ ID NO: 129), (GGGGS)5 (SEQ ID NO: 130), (AP)₂ (SEQ ID NO: 131), (AP)₅ (SEQ ID NO: 132), (AP)₁₀ (SEQ ID NO: 133), (AP)₂₀ (SEQ ID NO: 134) and A(EAAAK)₅AAA (SEQ ID NO: 135). The dimers and multimers may be linked to each other in a N-to C-direction. The use of naturally occurring as well as artificial peptide linkers to connect polypeptides into novel linked fusion polypeptides is well known in the literature (Hallewell et al., J Biol Chem 264, 5260-5268, 1989; Alfthan et al., Protein Eng. 8, 725-731, 1995; Robinson & Sauer, Biochemistry 35, 109-116, 1996; U.S. Pat. No. 5,856,456).

Half-Life Extending Moieties

The FN3 domains that specifically bind PD-L1 of the invention may incorporate other subunits for example via covalent interaction. In one aspect of the invention, the FN3 domains that specifically bind PD-L1 of the invention further comprise a half-life extending moiety. Exemplary half-life extending moieties are albumin, albumin variants, albumin-binding proteins and/or domains, transferrin and fragments and analogues thereof, and Fc regions. An exemplary albumin variant is shown in SEQ ID NO: 136. Amino acid sequences of the human Fc regions are well known, and include IgG1, IgG2, IgG3, IgG4, IgM, IgA and IgE Fc regions.

All or a portion of an antibody constant region may be attached to the FN3 domain that specifically binds PD-L1 of the invention to impart antibody-like properties, especially those properties associated with the Fc region, such as Fc effector functions such as Clq binding, complement dependent cytotoxicity (CDC), Fc receptor binding, antibody-dependent cell-mediated cytotoxicity (ADCC), phagocytosis, down regulation of cell surface receptors (e.g., B cell receptor; BCR), and may be further modified by modifying residues in the Fc responsible for these activities (for review; see Strohl, Curr Opin Biotechnol. 20, 685-691, 2009).

Additional moieties may be incorporated into the FN3 domains that specifically bind PD-L1 of the invention such as polyethylene glycol (PEG) molecules, such as PEG5000 or PEG20,000, fatty acids and fatty acid esters of different chain lengths, for example laurate, myristate, stearate, arachidate, behenate, oleate, arachidonate, octanedioic acid, tetradecanedioic acid, octadecanedioic acid, docosanedioic acid, and the like, polylysine, octane, carbohydrates (dextran, cellulose, oligo- or polysaccharides) for desired properties. These moieties may be direct fusions with the protein scaffold coding sequences and may be generated by standard cloning and expression techniques. Alternatively, well known chemical coupling methods may be used to attach the moieties to recombinantly produced molecules of the invention.

A pegyl moiety may for example be added to the FN3 domain that specifically binds PD-L1 of the invention by incorporating a cysteine residue to the C-terminus of the molecule, or engineering cysteines into residue positions that face away from the PD-L1 binding face of the molecule, and attaching a pegyl group to the cysteine using well known methods.

FN3 domains that specifically bind PD-L1 of the invention incorporating additional moieties may be compared for functionality by several well-known assays. For example, altered properties due to incorporation of Fc domains and/or Fc domain variants may be assayed in Fc receptor binding assays using soluble forms of the receptors, such as the FcγRI, FcγRII, FcγRIII or FcRn receptors, or using well known cell-based assays measuring for example ADCC or CDC, or evaluating pharmacokinetic properties of the molecules of the invention in in vivo models.

Polynucleotides, Vectors, Host Cells

The invention also provides nucleic acids encoding the FN3 domains specifically binding PD-L1 of the invention as isolated polynucleotides or as portions of expression vectors or as portions of linear DNA sequences, including linear DNA sequences used for in vitro transcription/translation, vectors compatible with prokaryotic, eukaryotic or filamentous phage expression, secretion and/or display of the compositions or directed mutagens thereof. Certain exemplary polynucleotides are disclosed herein, however, other polynucleotides which, given the degeneracy of the genetic code or codon preferences in a given expression system, encode the FN3 domains of the invention are also within the scope of the invention.

The invention also provides an isolated polynucleotide encoding the FN3 domain specifically binding PD-L1 comprising the amino acid sequence of SEQ ID NOs: 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123 or 124.

The polynucleotides of the invention may be produced by chemical synthesis such as solid phase polynucleotide synthesis on an automated polynucleotide synthesizer and assembled into complete single or double stranded molecules. Alternatively, the polynucleotides of the invention may be produced by other techniques such as PCR followed by routine cloning. Techniques for producing or obtaining polynucleotides of a given known sequence are well known in the art.

The polynucleotides of the invention may comprise at least one non-coding sequence, such as a promoter or enhancer sequence, intron, polyadenylation signal, a cis sequence facilitating RepA binding, and the like. The polynucleotide sequences may also comprise additional sequences encoding additional amino acids that encode for example a marker or a tag sequence such as a histidine tag or an HA tag to facilitate purification or detection of the protein, a signal sequence, a fusion protein partner such as RepA, Fc or bacteriophage coat protein such as pIX or pIII.

The invention also provides a vector comprising at least one polynucleotide of the invention. Such vectors may be plasmid vectors, viral vectors, vectors for baculovirus expression, transposon based vectors or any other vector suitable for introduction of the polynucleotides of the invention into a given organism or genetic background by any means. Such vectors may be expression vectors comprising nucleic acid sequence elements that can control, regulate, cause or permit expression of a polypeptide encoded by such a vector. Such elements may comprise transcriptional enhancer binding sites, RNA polymerase initiation sites, ribosome binding sites, and other sites that facilitate the expression of encoded polypeptides in a given expression system. Such expression systems may be cell-based, or cell-free systems well known in the art.

The invention also provides a host cell comprising the vector of the invention. The FN3 domain that specifically bind PD-L1 of the invention may be optionally produced by a cell line, a mixed cell line, an immortalized cell or clonal population of immortalized cells, as well known in the art. See, e.g., Ausubel, et al., ed., Current Protocols in Molecular Biology, John Wiley & Sons, Inc., NY, N.Y. (1987-2001); Sambrook, et al., Molecular Cloning: A Laboratory Manual, r^(d) Edition, Cold Spring Harbor, N.Y. (1989); Harlow and Lane, Antibodies, a Laboratory Manual, Cold Spring Harbor, N.Y. (1989); Colligan, et al., eds., Current Protocols in Immunology, John Wiley & Sons, Inc., NY (1994-2001); Colligan et al., Current Protocols in Protein Science, John Wiley & Sons, NY, NY, (1997-2001).

The host cell chosen for expression may be of mammalian origin or may be selected from COS-1, COS-7, HEK293, BHK21, CHO, BSC-1, He G2, SP2/0, HeLa, myeloma, lymphoma, yeast, insect or plant cells, or any derivative, immortalized or transformed cell thereof. Alternatively, the host cell may be selected from a species or organism incapable of glycosylating polypeptides, e.g. a prokaryotic cell or organism, such as BL21, BL21(DE3), BL21-GOLD(DE3), XL1-Blue, JM109, HMS174, HMS174(DE3), and any of the natural or engineered E. coli spp, Klebsiella spp., or Pseudomonas spp strains.

The invention also provides a method of producing the isolated FN3 domain that specifically binds PD-L1 of the invention, comprising culturing the isolated host cell of the invention under conditions such that the isolated FN3 domain that specifically binds PD-L1 is expressed, and purifying the FN3 domain.

The FN3 domains that specifically bind PD-L1 may be purified from recombinant cell cultures by well-known methods, for example by protein A purification, ammonium sulfate or ethanol precipitation, acid extraction, anion or cation exchange chromatography, phosphocellulose chromatography, hydrophobic interaction chromatography, affinity chromatography, hydroxylapatite chromatography and lectin chromatography, or high performance liquid chromatography (HPLC).

Anti-Idiotypic Antibodies

The present invention also provides an anti-idiotypic antibody binding to the FN3 domain of the invention.

The invention also provides an anti-idiotypic antibody that specifically binds the FN3 domain comprising any one of SEQ ID NOs: 34-124.

Kits

The invention also provides a kit comprising the FN3 domain that specifically binds PD-L1 of the invention.

The kit may be used for therapeutic uses and as a diagnostic kit.

In some embodiments, the kit comprises the FN3 domain that specifically binds PD-L1 of the invention and reagents for detecting the FN3 domain. The kit can include one or more other elements including: instructions for use; other reagents, e.g., a label, an agent useful for chelating, or otherwise coupling, a radioprotective composition; devices or other materials for preparing the FN3 domain that specifically binds PD-L1 of the invention for administration for imaging, diagnostic or therapeutic purpose; pharmaceutically acceptable carriers; and devices or other materials for administration to a subject.

In some embodiments, the kit comprises the FN3 domain that specifically binds PD-L1 comprising any one of SEQ ID NOs: 34-124.

Uses of PD-L1 Binding FN3 Domains of the Invention

The FN3 domains that specifically bind PD-L1 of the invention may be used to diagnose, monitor, modulate, treat, alleviate, help prevent the incidence of, or reduce the symptoms of human disease or specific pathologies in cells, tissues, organs, fluid, or, generally, a host. The FN3 domains that specifically bind PD-L1 of the invention may also be used in imaging PD-L1 positive tumor tissue in a subject. The methods of the invention may be used with an animal patient belonging to any classification. Examples of such animals include mammals such as humans, rodents, dogs, cats and farm animals.

The invention provides a method of diagnosing a subject having, or who is likely to develop cancer of a tissue based on the expression of PD-L1 by cells of the cancer tissue, methods of predicting success of immunotherapy, methods of prognosis, and methods of treatment.

The invention also provides a method of detecting PD-L1-expressing cancer cells in a tumor tissue, comprising

obtaining a sample of the tumor tissue from a subject;

detecting whether PD-L1 is expressed in the tumor tissue by contacting toe sample of the tumor tissues with the FN3 domain that specifically binds PD-L1 comprising the sequence of any one of SEQ ID NOs: 34-124 and detecting the binding between PD-L1 and the FN3 domain.

The tissue can be tissue of any organ or anatomical system, for example lung, epithelial, connective, vascular, muscle, neural, skeletal, lymphatic, prostate, cervical, breast, spleen, gastric, intestinal, oral, esophageal, uterine, ovarian, renal or testicular tissue.

PD-L1 expression may be evaluated using known methods such as immunohistochemistry or ELISA.

The invention also provides a method of isolating PD-L1 expressing cells, comprising

obtaining a sample from a subject;

contacting the sample with the FN3 domain that specifically binds PD-L1 comprising the sequence of any one of SEQ ID NOs: 34-124, and

isolating the cells bound to the FN3 domains.

The invention also provides a method of detecting PD-L1-expressing cancer cells in a tumor tissue, comprising

-   -   conjugating the FN3 domain that specifically binds PD-L1         comprising the     -   sequence of any one of SEQ ID NOs: 34-124 to a detectable label         to form a conjugate;     -   administering the conjugate to a subject; and     -   visualizing the PD-L1 expressing cancer cells to which the         conjugate is bound.

The invention also provides a method of treating a subject having cancer, comprising administering to the subject a FN3 domain that specifically binds PD-L1 of the invention.

In some embodiments, the subject has a solid tumor.

In some embodiments, the subject has a hematological malignancy.

In some embodiments, the solid tumor is a melanoma.

In some embodiments, the solid tumor is a lung cancer.

In some embodiments, the solid tumor is a non-small cell lung cancer (NSCLC).

In some embodiments, the solid tumor is a squamous non-small cell lung cancer (NSCLC).

In some embodiments, the solid tumor is a non-squamous NSCLC.

In some embodiments, the solid tumor is a lung adenocarcinoma.

In some embodiments, the solid tumor is a renal cell carcinoma (RCC).

In some embodiments, the solid tumor is a mesothelioma.

In some embodiments, the solid tumor is a nasopharyngeal carcinoma (NPC).

In some embodiments, the solid tumor is a colorectal cancer.

In some embodiments, the solid tumor is a prostate cancer.

In some embodiments, the solid tumor is castration-resistant prostate cancer.

In some embodiments, the solid tumor is a stomach cancer.

In some embodiments, the solid tumor is an ovarian cancer.

In some embodiments, the solid tumor is a gastric cancer.

In some embodiments, the solid tumor is a liver cancer.

In some embodiments, the solid tumor is pancreatic cancer.

In some embodiments, the solid tumor is a thyroid cancer.

In some embodiments, the solid tumor is a squamous cell carcinoma of the head and neck.

In some embodiments, the solid tumor is a carcinomas of the esophagus or gastrointestinal tract.

In some embodiments, the solid tumor is a breast cancer.

In some embodiments, the solid tumor is a fallopian tube cancer.

In some embodiments, the solid tumor is a brain cancer.

In some embodiments, the solid tumor is an urethral cancer.

In some embodiments, the solid tumor is a genitourinary cancer.

In some embodiments, the solid tumor is an endometriosis.

In some embodiments, the solid tumor is a cervical cancer.

In some embodiments, the solid tumor is a metastatic lesion of the cancer.

In some embodiments, the hematological malignancy is a lymphoma, a myeloma or a leukemia.

In some embodiments, the hematological malignancy is a B cell lymphoma.

In some embodiments, the hematological malignancy is Burkitt's lymphoma.

In some embodiments, the hematological malignancy is Hodgkin's lymphoma.

In some embodiments, the hematological malignancy is a non-Hodgkin's lymphoma.

In some embodiments, the hematological malignancy is a myelodysplastic syndrome.

In some embodiments, the hematological malignancy is an acute myeloid leukemia (AML).

In some embodiments, the hematological malignancy is a chronic myeloid leukemia (CML).

In some embodiments, the hematological malignancy is a chronic myelomoncytic leukemia (CMML).

In some embodiments, the hematological malignancy is a multiple myeloma (MM).

In some embodiments, the hematological malignancy is a plasmacytoma. In some embodiments, the cancer is kidney cancer.

“Treat” or “treatment” refers to both therapeutic treatment and prophylactic or preventative measures, wherein the object is to prevent or slow down (lessen) an undesired physiological change or disorder, such as the development or spread of cancer. For purposes of this invention, beneficial or desired clinical results include, but are not limited to, alleviation of symptoms, diminishment of extent of disease, stabilized (i.e., not worsening) state of disease, delay or slowing of disease progression, amelioration or palliation of the disease state, and remission (whether partial or total), whether detectable or undetectable. “Treatment” can also mean prolonging survival as compared to expected survival if not receiving treatment. Those in need of treatment include those already with the condition or disorder as well as those prone to have the condition or disorder or those in which the condition or disorder is to be prevented.

A “therapeutically effective amount” refers to an amount effective, at dosages and for periods of time necessary, to achieve a desired therapeutic result. A therapeutically effective amount of the FN3 domains that specifically bind PD-L1 of the invention may vary according to factors such as the disease state, age, sex, and weight of the individual. Exemplary indicators of an effective FN3 domain that specifically binds PD-L1 is improved well-being of the patient, decrease or shrinkage of the size of a tumor, arrested or slowed growth of a tumor, and/or absence of metastasis of cancer cells to other locations in the body.

Administration/Pharmaceutical Compositions

The invention provides for pharmaceutical compositions of the FN3 domains that specifically bind PD-L1, optionally conjugated to a detectable label or a cytotoxic drug of the invention and a pharmaceutically acceptable carrier. For therapeutic use, the FN3 domains that specifically bind PD-L1 of the invention may be prepared as pharmaceutical compositions containing an effective amount of the domain or molecule as an active ingredient in a pharmaceutically acceptable carrier. “Carrier” refers to a diluent, adjuvant, excipient, or vehicle with which the active compound is administered. Such vehicles can be liquids, such as water and oils, including those of petroleum, animal, vegetable or synthetic origin, such as peanut oil, soybean oil, mineral oil, sesame oil and the like. For example, 0.4% saline and 0.3% glycine can be used. These solutions are sterile and generally free of particulate matter. They may be sterilized by conventional, well-known sterilization techniques (e.g., filtration). The compositions may contain pharmaceutically acceptable auxiliary substances as required to approximate physiological conditions such as pH adjusting and buffering agents, stabilizing, thickening, lubricating and coloring agents, etc. The concentration of the molecules of the invention in such pharmaceutical formulation can vary widely, i.e., from less than about 0.5%, usually at least about 1% to as much as 15 or 20% by weight and will be selected primarily based on required dose, fluid volumes, viscosities, etc., according to the particular mode of administration selected. Suitable vehicles and formulations, inclusive of other human proteins, e.g., human serum albumin, are described, for example, in e.g. Remington: The Science and Practice of Pharmacy, 21′ Edition, Troy, D.B. ed., Lipincott Williams and Wilkins, Philadelphia, PA 2006, Part 5, Pharmaceutical Manufacturing pp 691-1092, See especially pp. 958-989.

The mode of administration for therapeutic use of the FN3 domains of the invention may be any suitable route that delivers the agent to the host, such as parenteral administration, e.g., intradermal, intramuscular, intraperitoneal, intravenous or subcutaneous, pulmonary; transmucosal (oral, intranasal, intravaginal, rectal), using a formulation in a tablet, capsule, solution, powder, gel, particle; and contained in a syringe, an implanted device, osmotic pump, cartridge, micropump; or other means appreciated by the skilled artisan, as well known in the art. Site specific administration may be achieved by for example intrarticular, intrabronchial, intraabdominal, intracapsular, intracartilaginous, intracavitary, intracelial, intracerebellar, intracerebroventricular, intracolic, intracervical, intragastric, intrahepatic, intracardial, intraosteal, intrapelvic, intrapericardiac, intraperitoneal, intrapleural, intraprostatic, intrapulmonary, intrarectal, intrarenal, intraretinal, intraspinal, intrasynovial, intrathoracic, intrauterine, intravascular, intravesical, intralesional, vaginal, rectal, buccal, sublingual, intranasal, or transdermal delivery.

Pharmaceutical compositions can be supplied as a kit comprising a container that comprises the pharmaceutical composition as described herein. A pharmaceutical composition can be provided, for example, in the form of an injectable solution for single or multiple doses, or as a sterile powder that will be reconstituted before injection. Alternatively, such a kit can include a dry-powder disperser, liquid aerosol generator, or nebulizer for administration of a pharmaceutical composition. Such a kit can further comprise written information on indications and usage of the pharmaceutical composition.

While having described the invention in general terms, the embodiments of the invention will be further disclosed in the following examples that should not be construed as limiting the scope of the claims.

EXAMPLE 1 Construction of Tencon Libraries with Randomized Loops

Tencon (SEQ ID NO: 1) is an immunoglobulin-like scaffold, fibronectin type III (FN3) domain, designed from a consensus sequence of fifteen FN3 domains from human tenascin-C (Jacobs et al., Protein Engineering, Design, and Selection, 25:107-117, 2012; U.S. Pat. No. 8,278,419). The crystal structure of Tencon shows six surface-exposed loops that connect seven beta-strands. These loops, or selected residues within each loop, can be randomized in order to construct libraries of fibronectin type III (FN3) domains that can be used to select novel molecules that bind to specific targets.

Tencon: (SEQ ID NO 1) LPAPKNLVVSEVTEDSLRLSWTAPDAAFDSFLIQYQESEKVGEAINLTVP GSERSYDLTGLKPGTEYTVSIYGVKGGHRSNPLSAEFTT: Various libraries were generated using the tencon scaffold and various design strategies. In general, libraries TCL1 and TCL2 produced good binders. Generation of TCL1 and TCL2 libraries are described in detail in Int. Pat. Publ. No. WO/2014081944A2. Construction of TCL1 Library

A library designed to randomize only the FG loop of Tencon (SEQ ID NO: 1), TCL1, was constructed for use with the cis-display system (Jacobs et al., Protein Engineering, Design, and Selection, 25:107-117, 2012). In this system, a single-strand DNA incorporating sequences for a Tac promoter, Tencon library coding sequence, RepA coding sequence, cis-element, and ori element is produced. Upon expression in an in vitro transcription/translation system, a complex is produced of the Tencon-RepA fusion protein bound in cis to the DNA from which it is encoded. Complexes that bind to a target molecule are then isolated and amplified by polymerase chain reaction (PCR), as described below.

Construction of the TCL1 library for use with cis-display was achieved by successive rounds of PCR to produce the final linear, double-stranded DNA molecules in two halves; the 5′ fragment contains the promoter and Tencon sequences, while the 3′ fragment contains the repA gene and the cis- and ori elements. These two halves are combined by restriction digest in order to produce the entire construct. The TCL1 library was designed to incorporate random amino acids only in the FG loop of Tencon, KGGHRSN (SEQ ID NO: 55). NNS codons were used in the construction of this library, resulting in the possible incorporation of all 20 amino acids and one stop codon into the FG loop. The TCL1 library contains six separate sub-libraries, each having a different randomized FG loop length, from 7 to 12 residues, in order to further increase diversity.

TCL1 library (SEQ ID NO: 2) LPAPKNLVVSEVTEDSLRLSWTAPDAAFDSFLIQYQESEKVGEAINLTVP GSERSYDLTGLKPGTEYTVSIYGVX₁X₂X₃X₄X₅X₆X₇X₈X₉X₁₀X₁₁  X₁₂ PLSAEFTT;  wherein X₁, X₂, X₃, X₄, X₅, X₆, X₇ is any amino acid; and X₈, X₉, X₁₀, X₁₁ and X₁₂ are any amino acid or deleted Construction of TCL2 Library

TCL2 library was constructed in which both the BC and the FG loops of Tencon were randomized and the distribution of amino acids at each position was strictly controlled. Table 3 shows the amino acid distribution at desired loop positions in the TCL2 library. The designed amino acid distribution had two aims. First, the library was biased toward residues that were predicted to be structurally important for Tencon folding and stability based on analysis of the Tencon crystal structure and/or from homology modeling. For example, position 29 was fixed to be only a subset of hydrophobic amino acids, as this residue was buried in the hydrophobic core of the Tencon fold. A second layer of design included biasing the amino acid distribution toward that of residues preferentially found in the heavy chain HCDR3 of antibodies, to efficiently produce high-affinity binders (Birtalan et al., J Mol Biol 377:1518-28, 2008; Olson et al., Protein Sci 16:476-84, 2007). Towards this goal, the “designed distribution” in Table 2 refers to the distribution as follows: 6% alanine, 6% arginine, 3.9% asparagine, 7.5% aspartic acid, 2.5% glutamic acid, 1.5% glutamine, 15% glycine, 2.3% histidine, 2.5% isoleucine, 5% leucine, 1.5% lysine, 2.5% phenylalanine, 4% proline, 10% serine, 4.5% threonine, 4% tryptophan, 17.3% tyrosine, and 4% valine. This distribution is devoid of methionine, cysteine, and STOP codons.

TCL2 library (SEQ ID NO: 3) LPAPKNLVVSEVTEDSLRLSWX₁X₂X₃X₄X₅X₆X₇X₈SFLIQYQESEKVG EAINLTVPGSERSYDLTGLKPGTEYTVSIYGVX₉X₁₀X₁₁X₁₂X₁₃SX₁₄  X₁₅LSAEFTT; wherein X₁ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₂ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₃ Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₄ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₅ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₆ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₇ is Phe, Ile, Leu, Val or Tyr; X₈ is Asp, Glu or Thr; X₉ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₁₀ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₁₁ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₁₂ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₁₃ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₁₄ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; and X₁₅ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val.

TABLE 2 Residue Position* WT residues Distribution in the TCL2 library 22 T designed distribution 23 A designed distribution 24 P 50% P + designed distribution 25 D designed distribution 26 A 20% A + 20% G + designed distribution 27 A designed distribution 28 F 20% F, 20% I, 20% L, 20% V, 20% Y 29 D 33% D, 33% E, 33% T 75 K designed distribution 76 G designed distribution 77 G designed distribution 78 H designed distribution 79 R designed distribution 80 S 100% S 81 N designed distribution 82 P 50% P + designed distribution *residue numbering is based on Tencon sequence of SEQ ID NO: 1

Subsequently, these libraries were improved by various ways, including building of the libraries on a stabilized Tencon framework (U.S. Pat. No. 8,569,227) that incorporates substitutions El1R/L17A/N46V/E861 (Tencon27; SEQ ID NO: 4) when compared to the wild type tencon as well as altering of the positions randomized in the BC and FG loops. Tencon27 is described in Int. Pat. Appl. No. WO2013049275. From this, new libraries designed to randomize only the FG loop of Tencon (library TCL9), or a combination of the BC and FG loops (library TCL7) were generated. These libraries were constructed for use with the cis-display system (Odegrip et al., Proc Natl Acad Sci U S A 101: 2806-2810, 2004). The details of this design are shown below:

Stabilized Tencon (Tencon27) (SEQ ID NO: 4) LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFLIQYQESEKVGEAIVLTVP GSERSYDLTGLKPGTEYTVSIYGVKGGHRSNPLSAIFTT TCL7 (randomized FG and BC loops) (SEQ ID NO: 5) LPAPKNLVVSRVTEDSARLSWX₁X₂X₃X₄X₅X₆X₇X₈X₉FDSFLIQYQES EKVGEAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVX₁₀X₁₁X₁₂X₁₃  X₁₄X₁₅X₁₆X₁₇X₁₈X₁₉SNPLSAIFTT; wherein X₁, X₂, X₃, X₄, X₅, X₆, X₁₀, X₁₁, X₁₂, X₁₃, X₁₄, X₁₅ and X₁₆ is A, D, E, F, G, H, I, K, L, N, P, Q, R, S, T, V, W or Y; and X₇, X₈, X₉, X₁₇, X₁₈ and X₁₉, is A, D, E, F, G, H, I, K, L, N, P, Q, R, S, T, V, W, Y or deleted. TCL9 (randomized FG loop) (SEQ ID NO: 6) LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFLIQYQESEKVGEAIVLTVP GSERSYDLTGLKPGTEYTVSIYGV XX₂X₃X₄X₅X₆X₇X₈X₉ X₁₀X₁₁  X₁₂SNPLSAIFTT; X₁, X₂, X₃, X₄, X₅, X₆ and X₇, is A, D, E, F, G, H, I, K, L, N, P, Q, R, S, T, V, W or Y; and X₈, X₉, X₁₀, X₁₁ and X₁₂ is A, D, E, F, G, H, I, K, L, N, P, Q, R, S, T, V, W, Y or deleted.

For library construction, DNA fragments encoding randomized BC loops (lengths 6-9 positions) or FG loops (lengths 7-12 positions) were synthesized using Slonomics technology (Sloning Biotechnology GmbH) so as to control the amino acid distribution of the library and to eliminate stop codons. Two different sets of DNA molecules randomizing either the BC loop or the FG loops were synthesized independently and later combined using PCR to produce the full library product.

Construction of FG Loop Libraries (TCL9)

A set of synthetic DNA molecules consisting of a 5′ Tac promoter followed by the complete gene sequence of Tencon with the exception of randomized codons in the FG loop was produced (SEQ ID NOs: 26-31). For FG loop randomization, all amino acids except cysteine and methionine were encoded at equal percentages. The lengths of the diversified portion are such that they encode for 7, 8, 9, 10, 11, or 12 amino acids in the FG loop. Sub-libraries of each length variation were synthesized individually at a scale of 2 ug and then amplified by PCR using oligos Sloning-FOR (SEQ ID NO: 9) and Sloning-Rev (SEQ ID NO: 10).

The 3′ fragment of the library is a constant DNA sequence containing elements for display, including a PspOMI restriction site, the coding region of the repA gene, and the cis- and ori elements. PCR reactions were performed to amplify this fragment using a plasmid (pCR4Blunt) (Invitrogen) as a template with M13 Forward and M13 Reverse primers. The resulting PCR products were digested by PspOMI overnight and gel-purified. To ligate the 5′ portion of library DNA to the 3′ DNA containing repA gene, 2 pmol (˜540 ng to 560 ng) of 5′ DNA was ligated to an equal molar (˜1.25 ug) of 3′ repA DNA in the presence of NotI and PspOMI enzyme and T4 ligase at 37° C. overnight. The ligated library product was amplified by using 12 cycles of PCR with oligos POP2250 (SEQ ID NO: 11) and DigLigRev (SEQ ID NO: 12). For each sub-library, the resulting DNA from 12 PCR reactions were combined and purified by Qiagen spin column The yield for each sub-library of TCL9 ranged from 32-34 _(l)ag.

Construction of FG/BC Loop Libraries (TCL7)

The TCL7 library provides for a library with randomized Tencon BC and FG loops. In this library, BC loops of lengths 6-9 amino acids were mixed combinatorially with randomized FG loops of 7-12 amino acids in length. Synthetic Tencon fragments BC6, BC7, BC8, and BC9 (SEQ ID NOs: 13-16, respectively) were produced to include the Tencon gene encoding for the N-terminal portion of the protein up to and including residue VX such that the BC loop is replaced with either 6, 7, 8, or 9 randomized amino acids. These fragments were synthesized prior to the discovery of L17A, N46V and E831 mutations (CEN5243) but these mutations were introduced in the molecular biology steps described below. In order to combine this fragment with fragments encoding for randomized FG loops, the following steps were taken.

First, a DNA fragment encoding the Tac promoter and the 5′ sequence of Tencon up to the nucleotide encoding for amino acid A17 (130mer-L17A, SEQ ID NO: 17) was produced by PCR using oligos POP2222ext (SEQ ID NO: 18) and LS1114 (SEQ ID NO: 19). This was done to include the L17A mutation in the library (CEN5243). Next, DNA fragments encoding for Tencon residues R18-V75 including randomized BC loops were amplified by PCR using BC6, BC7, BC8, or BC9 as a templates and oligos LS1115 (SEQ ID NO: 20) and LS1117 (SEQ ID NO: 21). This PCR step introduced a Bsal site at the 3′ end. These DNA fragments were subsequently joined by overlapping PCR using oligos POP2222ext and LS1117 as primers. The resulting PCR product of 240 bp was pooled and purified by Qiagen PCR purification kit. The purified DNA was digested with Bsal-HF and gel purified.

Fragments encoding the FG loop were amplified by PCR using FG7, FG8, FG9, FG10, FG11, and FG12 as templates with oligonucleotides SDG10 (SEQ ID NO: 22) and SDG24 (SEQ ID NO: 23) to incorporate a Bsal restriction site and N46V and E86I variations (CEN5243).

The digested BC fragments and FG fragments were ligated together in a single step using a 3-way ligation. Four ligation reactions in the 16 possible combinations were set up, with each ligation reaction combining two BC loop lengths with 2 FG loop lengths. Each ligation contained—300 ng of total BC fragment and 300 ng of the FG fragment. These 4 ligation pools were then amplified by PCR using oligos POP2222 (SEQ ID NO: 24) and SDG28 SEQ ID N: 25). 7.5 _(l)ag of each reaction product were then digested with Notl and cleaned up with a Qiagen PCR purification column. 5.2 _(l)ag of this DNA, was ligated to an equal molar amount of RepA DNA fragment (˜14 _(l)ig) digested with PspOMI and the product amplified by PCR using oligos POP2222.

EXAMPLE 2 Generation of Tencon Libraries having Alternative Binding Surfaces

The choice of residues to be randomized in a particular library design governs the overall shape of the interaction surface created. X-ray crystallographic analysis of an FN3 domain containing scaffold protein selected to bind maltose binding protein (MBP) from a library in which the BC, DE, and FG loops were randomized was shown to have a largely curved interface that fits into the active site of MBP (Koide et al., Proc Natl Acad Sci U S A 104: 6632-6637, 2007). In contrast, an ankyrin repeat scaffold protein that was selected to bind to MBP was found to have a much more planar interaction surface and to bind to the outer surface of MBP distant from the active (Binz et al., Nat Biotechnol 22: 575-582, 2004). These results suggest that the shape of the binding surface of a scaffold molecule (curved vs. flat) may dictate what target proteins or specific epitopes on those target proteins are able to be bound effectively by the scaffold. Published efforts around engineering protein scaffolds containing FN3 domains for protein binding has relied on engineering adjacent loops for target binding, thus producing curved binding surfaces. This approach may limit the number of targets and epitopes accessible by such scaffolds.

Tencon and other FN3 domains contain two sets of CDR-like loops lying on the opposite faces of the molecule, the first set formed by the BC, DE, and FG loops, and the second set formed by the AB, CD, and EF loops. The two sets of loops are separated by the beta-strands that form the center of the FN3 structure. If the image of the Tencon is rotated by 90 degrees, an alternative surface can be visualized. This slightly concave surface is formed by the CD and FG loops and two antiparallel beta- strands, the C and the F beta-strands, and is herein called the C-CD-F-FG surface. The C-CD-F-FG surface can be used as a template to design libraries of protein scaffold interaction surfaces by randomizing a subset of residues that form the surface. Beta-strands have a repeating structure with the side chain of every other residue exposed to the surface of the protein. Thus, a library can be made by randomizing some or all surface exposed residues in the beta strands. By choosing the appropriate residues in the beta-strands, the inherent stability of the Tencon scaffold should be minimally compromised while providing a unique scaffold surface for interaction with other proteins.

Library TCL14 (SEQ ID NO: 7), was designed into Tencon27 scaffold (SEQ ID NO: 4).

A full description of the methods used to construct this library is described in US. Pat. Publ. No. US2013/0226834.

TCL14 library (SEQ ID NO: 7): LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFX₁IX₂YX₃EX₄X₅X₆X₇GE AIVLTVPGSERSYDLTGLKPGTEYX₈VX₉IX₁₀GVKGGX₁₁X₁₂SX₁₃PL SAIFTT; wherein X₁, X₂, X₃, X₄, X₅, X₆, X₇, X₈, X₉, X₁₀, X₁₁, X₁₂  and X₁₃ are A, D, E, F, G, H, I, K, L, N, P, Q, R, S, T, V, W, Y, C or M.

The two beta strands forming the C-CD-F-FG surface in Tencon27 have a total of 9 surface exposed residues that could be randomized; C-strand: S30, L32, Q34, Q36; F-strand: E66, T68, S70, Y72, and V74, while the CD loop has 6 potential residues: S38, E39, K40, V41, G42, and E43 and the FG loop has 7 potential residues: K75, G76, G77, H78, R79, S80, and N81. Select residues were chosen for inclusion in the TCL14 design due to the larger theoretical size of the library if all 22 residues were randomized.

Thirteen positions in Tencon were chosen for randomizing: L32, Q34 and Q36 in C-strand, S38, E39, K40 and V41 in CD-loop, T68, S70 and Y72 in F-strand, H78, R79, and N81 in FG-loop. In the C and F strands S30 and E66 were not randomized as they lie just beyond the CD and FG loops and do not appear to be as apparently a part of the C-CD-F-FG surface. For the CD loop, G42 and E43 were not randomized as glycine, providing flexibility, can be valuable in loop regions, and E43 lies at the junction of the surface. The FG loop had K75, G76, G77, and S80 excluded. The glycines were excluded for the reasons above while careful inspection of the crystal structures revealed S80 making key contacts with the core to help form the stable FG loop. K75 faces away from the surface of the C-CD-F-FG surface and was a less appealing candidate for randomization. Although the above mentioned residues were not randomized in the original TCL14 design, they could be included in subsequent library designs to provide additional diversity for de novo selection or for example for an affinity maturation library on a select TCL14 target specific hit.

Subsequent to the production of TCL14, 3 additional Tencon libraries of similar design were produced. These two libraries, TCL19, TCL21 and TCL23, are randomized at the same positions as TCL14 (see above) however the distribution of amino acids occurring at these positions is altered (Table 3). TCL19 and TCL21 were designed to include an equal distribution of 18 natural amino acids at every position (5.55% of each), excluding only cysteine and methionine. TCL23 was designed such that each randomized position approximates the amino acid distribution found in the HCDR3 loops of functional antibodies (Birtalan et al., J Mol Biol 377: 1518-1528, 2008) as described in Table 3. As with the TCL21 library, cysteine and methionine were excluded.

A third additional library was built to expand potential target binding surface of the other libraries library. In this library, TCL24, 4 additional Tencon positions were randomized as compared to libraries TCL14, TCL19, TCL21, and TCL23. These positions include N46 and T48 from the D strand and S84 and 186 from the G strand. Positions 46, 48, 84, and 86 were chosen in particular as the side chains of these residues are surface exposed from beta-strands D and G and lie structurally adjacent to the randomized portions of the C and F strand, thus increasing the surface area accessible for binding to target proteins. The amino acid distribution used at each position for TCL24 is identical to that described for TCL19 and TCL21 in Table 3.

TCL24 Library (SEQ ID NO: 8) LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFX₁IX₂YX₃EX₄X₅X₆X₇GE AIX₈LX₉VPGSERSYDLTGLKPGTEYX₁₀VX₁₁IX₁₂GVKGGX₁₃X₁₄S X₁₅PLX₁₆AX₁₇FTT; wherein X₁, X₂, X₃, X₄, X₅, X₆, X₁₀, X₁₁, X₁₂, X₁₃, X₁₄, X₁₅, X₁₆ and X₁₇ are A, D, E, F, G, H, I, K, L, N, P, Q, R, S, T, V, Y or W.

TABLE 3 Amino acid frequency (%) at each randomized position for TCL21, TCL23, and TCL24. Amino Acid TCL19 TCL21 TCL23 TCL24 Ala 5.6 5.6 6.0 5.6 Arg 5.6 5.6 6.0 5.6 Asn 5.6 5.6 3.9 5.6 Asp 5.6 5.6 7.5 5.6 Cys 0.0 0.0 0.0 0.0 Gln 5.6 5.6 1.5 5.6 Glu 5.6 5.6 2.5 5.6 Gly 5.6 5.6 15.0 5.6 His 5.6 5.6 2.3 5.6 Ile 5.6 5.6 2.5 5.6 Leu 5.6 5.6 5.0 5.6 Lys 5.6 5.6 1.5 5.6 Met 0.0 0.0 0.0 0.0 Phe 5.6 5.6 2.5 5.6 Pro 5.6 5.6 4.0 5.6 Ser 5.6 5.6 10.0 5.6 Thr 5.6 5.6 4.5 5.6 Trp 5.6 5.6 4.0 5.6 Tyr 5.6 5.6 17.3 5.6 Val 5.6 5.6 4.0 5.6 Generation of TCL21, TCL23, and TCL24 Libraries

The TCL21 library was generated using Colibra library technology (Isogenica) in order to control amino acid distributions. TCL19, TCL23, and TCL24 gene fragments were generated using Slonomics technology (Morphosys) to control amino acid distributions. PCR was used to amplify each library following initial synthesis followed by ligation to the gene for RepA in order to be used in selections using the CIS-display system (Odegrip et al., Proc Natl Acad Sci U S A 101: 2806-2810, 2004) as described above for the loop libraries.

EXAMPLE 3 Selection of Fibronectin Type III (FN3) Domains that Bind PD-L1 Panning

FN3 domains specific for human PD-L1 were selected via CIS-Display (Odegrip et al 2004) using recombinant biotinylated PD-L1 (rhPD-L1/Fc Chimera, R&D Systems 156-B7). For in vitro transcription and translation (ITT), 3μg of DNA from libraries TCL18, TCL19, TCL21, TCL23, and TCL24 were incubated at 30° C. with 0.1 mM complete amino acids, 1X S30 premix components, and 15 μL of S30 extract (Isogenica) in a total volume of 50 μL. After 1 hour, 375 μL of blocking solution (2% BSA in PBS, Invitrogen) was added and reactions were incubated on a cold block for 15 minutes. Unbound library members were removed by successive washes with TBST and TBS. After washing, DNA was eluted from the target protein by heating to 75° C. for 10 minutes and amplified by PCR using KOD polymerase for further rounds of panning High affinity binders were isolated by successively lowering the concentration of target PD-L1 during each round from 400 nM to 100 nM and increasing the washing stringency.

Outputs from the fifth round panning were subjected to four additional rounds of off-rate selection. Library transcription and translation was performed as described above after which the ITT reactions were incubated with biotinylated recombinant PD-L1 proteins and captured on neutravidin or streptavidin coated magnetic beads, before being washed in TBST extensively then subsequently washed in 5 μM cold recombinant PD-L1 protein for 1 hour. The biotinylated target antigen concentration was reduced from 25 nM in rounds 6 and 7 to 2.5 nM in rounds 8 and 9.

Following panning, genes encoding the selected FN3 domains were amplified by PCR, subcloned into a pET vector modified to include a ligase independent cloning site, and transformed into BL21 (DE3) (Stratagene) cells for soluble expression in E. coli using standard molecular biology techniques. A gene sequence encoding a C-terminal poly-histidine tag was added to each FN3 domain to enable purification and detection. Cultures were grown to an optical density of 0.6-0.8 in TB medium supplemented with 100 μg/mL carbenicillin in 1 mL 96-well blocks at 37° C. before the addition of IPTG to 1 mM, at which point the temperature was reduced to 30° C. Cells were harvested approximately 16 hours later by centrifugation and frozen at −20° C. Cell lysis was achieved by incubating each pellet in 0.6 mL of BugBuster® HT lysis buffer (Novagen EMD Biosciences) supplemented with 0.2 mg/mL lysozyme with shaking at room temperature for 30 minutes.

Biochemical Screening for FN3 Domains that Bind Recombinant PD-L1

Streptavidin-coated Maxisorp plates (Nunc catalog 436110) were blocked for lh in Starting Block T20 (Pierce) and then coated with biotinylated PD-L1 (using same antigen as in panning) or negative controls (an unrelated Fc-fused recombinant protein and human serum albumin) for lh. Plates were rinsed with TBST and diluted lysate was applied to plates for 1h. Following additional rinses, wells were treated with HRP-conjugated anti-FN3 domain antibody (PAB25) for lh and then assayed with POD (Roche catalog 11582950001). The DNA from FN3 domain lysates with ELISA binding signals to PD-L1 at least 5-fold above both Fc and HSA controls were sequenced resulting in 57 (Table 4) and 37 (Table 5) unique, readable FN3 domain sequences isolated from Round 5 and Round 9 screening respectively.

High-throughput Expression of Anti-PD-L1 FN3 Domains

40 isolated clones from unique hits identified by biochemical binding ELISA from Round 9 were combined for growth into 96-well block plate; clones grew in 1 mL cultures (LB media supplemented with kanamycin for selection) at 37° C. overnight with shaking. For protein expression in 96-block plates, 1 mL TB media supplemented with kanamycin was inoculated with 50 μL of the overnight culture and grown at 37° C. with continual shaking at 300rpm until OD600 =0.6-1. Once the target OD was reached, protein expression was induced with addition of IPTG to 1 mM; plates were transferred to 30° C. (300 rpm) for overnight growth. Overnight cultures were centrifuged to harvest the cells; bacterial pellets were stored at −80° C. until ready for use. Pellets were lysed with BugBuster® HT lysis buffer (Novagen EMD Biosciences) and His-tagged Centyrins purified from the clarified lysates with His MultiTrap™ HP plates (GE Healthcare) and eluted in buffer containing 20 mM sodium phosphate, 500 mM sodium chloride, and 250 mM imidazole at pH 7.4. Purified samples were exchanged into PBS pH 7.4 for analysis using PD MultiTrap™ G-25 plates (GE Healthcare).

Size Exclusion Chromatography Analysis

Size exclusion chromatography was used to determine the aggregation state of anti-PD-L1 FN3 domains Aliquots (10)(L) of each purified FN3 domain were injected onto a Superdex 75 5/150 column (GE Healthcare) at a flow rate of 0.3 mL/min in a mobile phase of PBS pH 7.4. Elution from the column was monitored by absorbance at 280 nm. Tencon protein was included in each run as a control. Agilent ChemStation software was used to analyse the elution profiles. 20 anti-PD-L1 FN3 domains demonstrated a retention time between 5.2 and 6.4 minutes and only a single SEC peak indicative of monomeric protein (Table 6).

TABLE 4 ELISA ELISA Fc ELISA SEQ PD-L1 Fc Control HSA ID Clone (RSU) (RSU) (RSU) NO: ISOP121HR5P1G9 17760 880 1760 34 ISOP121BR5P1F7 12880 720 880 35 ISOP121BR5P1A6 10960 720 720 36 ISOP121BR5P1C5 11680 400 720 37 ISOP121BR5P1D7 12800 800 720 38 ISOP121BR5P1C6 13360 720 720 39 ISOP121AR5P1G6 16960 1200 880 40 ISOP121BR5P1B7 11360 640 480 41 ISOP121FR5P1G1 10000 640 400 42 ISOP121GR5P1B4 16160 800 560 43 ISOP121BR5P1G2 16720 800 560 44 ISOP121HR5P1H2 20960 720 560 45 ISOP121FR5P1G11 18560 880 480 46 ISOP121AR5P1E7 327200 4240 6560 47 ISOP121GR5P1F6 32080 640 640 48 ISOP121BR5P1E9 42000 960 800 49 ISOP121AR5P1F2 51040 880 960 50 ISOP121AR5P1F7 64000 720 1040 51 ISOP121BR5P1H6 74640 1440 1040 52 ISOP121GR5P1A2 61680 720 720 53 ISOP121BR5P1D3 75760 800 800 54 ISOP121AR5P1F9 136080 1120 1040 55 ISOP121AR5P1H5 170800 960 1120 56 ISOP121AR5P1G10 231920 1360 1280 57 ISOP121AR5P1F3 180160 800 960 58 ISOP121BR5P1E2 137280 800 720 59 ISOP121BR5P1D1 186240 1040 960 60 ISOP121BR5P1C9 226400 1120 1040 61 ISOP121GR5P1G11 239600 960 1040 62 ISOP121BR5P1A7 388640 800 1120 63 ISOP121BR5P1C3 177040 640 480 64 ISOP121AR5P1D11 392800 640 1040 65 ISOP121ER5P1E7 251120 480 560 66 ISOP121GR5P1G7 367760 800 800 67 ISOP121AR5P1A8 515920 560 1040 68 ISOP121BR5P1E7 411760 800 640 69 ISOP121FR5P1H8 430640 560 640 70 ISOP121GR5P1D2 513280 720 640 71 ISOP121AR5P1H2 926720 880 1120 72 ISOP121GR5P1F10 577120 640 640 73 ISOP121BR5P1A2 742800 720 800 74 ISOP121GR5P1F7 697200 640 720 75 ISOP121AR5P1B8 591600 640 560 76 ISOP121GR5P1D7 791920 720 720 77 ISOP121BR5P1G3 770800 560 640 78 ISOP121AR5P1C5 732480 640 560 79 ISOP121FR5P1H9 1195520 720 880 80 ISOP121AR5P1A10 788560 1120 560 81 ISOP121HR5P1F2 906960 480 640 82 ISOP121AR5P1H1 1475280 880 880 83 ISOP121BR5P1D10 1538800 480 880 84 ISOP121BR5P1F10 1422880 560 720 85 ISOP121BR5P1D11 2442960 800 1120 86 ISOP121AR5P1E11 1842000 720 720 87 ISOP121BR5P1D6 2435760 560 880 88 ISOP121BR5P1B5 1483520 720 400 89

TABLE 5 ELISA ELISA Fc ELISA SEQ PD-L1 Fc Control HSA ID Clone (RSU) (RSU) (RSU) NO: ISOP194ER9P1G3 4288320 560 720 90 ISOP194AR9P1F2 16271040 1920 7520 91 ISOP194AR9P1H10 5212800 4400 2400 92 ISOP194BR9P1H4 4064960 3040 3840 93 ISOP194AR9P1D8 923200 12000 6560 94 ISOP194BR9P1D1 2152080 1360 1280 95 ISOP194AR9P1E8 3404480 6960 67680 96 ISOP194AR9P1E9 19719920 5520 1600 97 ISOP194AR9P1H9 2592720 21280 11360 98 ISOP194BR9P1A9 19046640 2320 3200 99 ISOP194BR9P1A5 3182000 800 1280 100 ISOP194BR9P1F7 15151120 1920 1760 101 ISOP194AR9P1G7 15914000 1280 560 102 ISOP194AR9P1E3 4566880 1120 800 103 ISOP194AR9P1C5 4371120 3440 1040 104 ISOP194AR9P1H3 17746800 9200 4880 105 ISOP194GR9P1E9 2821920 720 1200 106 ISOP194HR9P1B10 385360 560 1840 107 ISOP194ER9P1A11 4352240 800 880 108 ISOP194ER9P1A3 2360160 560 800 109 ISOP194ER9P1H9 3042800 720 880 110 ISOP194HR9P1B2 5656400 400 1840 111 ISOP194HR9P1D11 6620160 480 1680 112 ISOP194GR9P1F6 319200 400 1200 113 ISOP194GR9P1F9 105280 320 800 114 ISOP194GR9P1C11 164320 1040 1440 115 ISOP194ER9P1E6 8982160 240 720 116 ISOP194BR9P1G9 14376560 640 960 117 ISOP194BR9P1E4 9791680 640 1440 118 ISOP194AR9P1H1 21445040 15680 6800 119 ISOP194BR9P1D10 1666880 720 1120 120 ISOP194BR9P1C8 6110640 640 1280 121 ISOP194AR9P1C10 13863040 38240 14960 122 ISOP194AR9P1D11 1043280 28160 12720 123 ISOP194AR9P1C3 3548240 56400 5920 124

TABLE 6 SEC SEC Peak SEQ Retention Height ID Clone Time (min) (mAU) Monomeric? NO: ISOP194ER9P1G3 5.951 167.47 FALSE 90 ISOP194AR9P1F2 5.901 552.30 TRUE 91 ISOP194AR9P1H10 5.976 12.80 FALSE 92 ISOP194BR9P1H4 5.688 394.40 TRUE 93 ISOP194AR9P1D8 5.711 162.07 FALSE 94 ISOP194BR9P1D1 6.696 88.56 TRUE 95 ISOP194AR9P1E8 5.549 570.07 TRUE 96 ISOP194AR9P1E9 5.79  493.72 TRUE 97 ISOP194AR9P1H9 5.694 511.99 TRUE 98 ISOP194BR9P1A9 5.662 225.76 FALSE 99 ISOP194BR9P1A5 7.82  15.28 FALSE 100 ISOP194BR9P1F7 5.982 94.57 TRUE 101 ISOP194AR9P1G7 5.845 50.19 TRUE 102 ISOP194AR9P1E3 6.939 15.65 FALSE 103 ISOP194AR9P1C5 No peak FALSE 104 ISOP194AR9P1H3 6.238 155.66 TRUE 105 ISOP194GR9P1E9 6.343 20.59 TRUE 106 ISOP194HR9P1B10 5.911 398.72 TRUE 107 ISOP194ER9P1A11 5.957 154.65 TRUE 108 ISOP194ER9P1A3 5.976 341.20 TRUE 109 ISOP194ER9P1H9 No peak FALSE 110 ISOP194HR9P1B2 6.274 2.33 FALSE 111 ISOP194HR9P1D11 6.002 433.98 FALSE 112 ISOP194GR9P1F6 6.12  29.42 TRUE 113 ISOP194GR9P1F9 No peak FALSE 114 ISOP194GR9P1C11 12.458  2.90 FALSE 115 ISOP194ER9P1E6 6.125 149.28 TRUE 116 ISOP194BR9P1G9 6.622 84.28 FALSE 117 ISOP194BR9P1E4 5.714 456.33 TRUE 118 ISOP194AR9P1H1 6.247 12.76 FALSE 119 ISOP194BR9P1D10 6.059 10.60 FALSE 120 ISOP194BR9P1C8 No peak FALSE 121 ISOP194AR9P1C10 5.715 98.64 TRUE 122 ISOP194AR9P1D11 No peak FALSE 123 ISOP194AR9P1C3 5.588 700.26 TRUE 124

Sequences SEQ ID No. 1 = Original Tencon Sequence LPAPKNLVVSEVTEDSLRLSWTAPDAAFDSFLIQYQESEKVGEAINLTVPGSERSY DLTGLKPGTEYTVSIYGVKGGHRSNPLSAEFTT SEQ ID No. 2 = TCL1 library LPAPKNLVVSEVTEDSLRLSWTAPDAAFDSFLIQYQESEKVGEAINLTVPGSERSY DLTGLKPGTEYTVSIYGVX₁X₂X₃X₄X₅X₆X₇X₈X₉X₁₀X₁₁X₁₂ PLSAEFTT; wherein X₁, X₂, X₃, X₄, X₅, X₆, X₇ is any amino acid; and X₈, X₉, X₁₀, X₁₁ and X₁₂ are any amino acid or deleted SEQ ID No. 3 = TCL2 library LPAPKNLVVSEVTEDSLRLSWX₁X₂X₃X₄X₅X₆X₇X₈SFLIQYQESEKVGEAINLTVPGS ERSYDLTGLKPGTEYTVSIYGVX₉X₁₀X₁₁X₁₂X₁₃5X₁₄X₁₅LSAEFTT; wherein X₁ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₂ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₃ Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₄ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₅ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₆ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₇ is Phe, Ile, Leu, Val or Tyr; X₈ is Asp, Glu or Thr; X₉ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₁₀ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₁₁ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₁₂ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₁₃ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; X₁₄ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val; and X₁₅ is Ala, Arg, Asn, Asp, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Ser, Thr, Trp, Tyr or Val. SEQ ID No. 4 = Stabilized Tencon LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFLIQYQESEKVGEAIVLTVPGSERSY DLTGLKPGTEYTVSIYGVKGGHRSNPLSAIFTT SEQ ID No. 5 = TCL7 (FG and BC loops) LPAPKNLVVSRVTEDSARLSWX₁X₂X₃X₄X₅X₆X₇X₈X₉FDSFLIQYQESEKVGEAIVLT VPGSERSYDLTGLKPGTEYTVSIYGVX₁₀X₁₁X₁₂X₁₃X₁₄X₁₅X₁₆X₁₇X₁₈X₁₉SNPLSAIFTT; wherein X₁, X₂, X₃, X₄, X₅, X₆, X₁₀, X₁₁, X₁₂, X₁₃, X₁₄, X₁₅ and X₁₆ are A, D, E, F, G, H, I, K, L, N, P, Q, R, S, T, V, W or Y; and X₇, X₈, X₉, X₁₇, X₁₈ and X₁₉, are A, D, E, F, G, H, I, K, L, N, P, Q, R, S, T, V, W, Y or deleted SEQ ID No. 6 = TCL9 (FG loop) LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFLIQYQESEKVGEAIVLTVPGSERSY DLTGLKPGTEYTVSIYGVX₁X₂X₃X₄X₅X₆X₇X₈X₉X₁₀X₁₁X₁₂SNPLSAIFTT; wherein X₁, X₂, X₃, X₄, X₅, X₆ and X₇, is A, D, E, F, G, H, I, K, L, N, P, Q, R, S, T, V, W or Y; and X₈, X₉, X₁₀, X₁₁ and X₁₂ is A, D, E, F, G, H, I, K, L, N, P, Q, R, S, T, V, W, Y or deleted. TCL14 library (SEQ ID NO: 7): LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFX₁IX₂YX₃EX₄X₅X₆X₇GEAIVLTVPGS ERSYDLTGLKPGTEYX₈VX₉IX₁₀GVKGGX₁₁X₁₂SX₁₃PLSAIFTT; wherein X₁, X₂, X₃, X₄, X₅, X₆, X₇, X₈, X₉, X₁₀, X₁₁, X₁₂ and X₁₃ are A, D, E, F, G, H, I, K, L, N, P, Q, R, S, T, V, W, Y, C or M. TCL24 Library (SEQ ID NO: 8) LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFX₁IX₂YX₃EX₄X₅X₆X₇GEAIX₈LX₉VPG SERSYDLTGLKPGTEYX₁₀VX₁₁IX₁₂GVKGGX₁₃X₁₄SX₁₅PLX₁₆AX₁₇FTT; wherein X₁, X₂, X₃, X₄, X₅, X₆, X₁₀, X₁₁, X₁₂, X₁₃, X₁₄, X₁₅, X₁₆ and X₁₇ are A, D, E, F, G, H, I, K, L, N, P, Q, R, S, T, V, Y or W. SEQ ID No. 9 = Sloning-FOR GTGACACGGCGGTTAGAAC SEQ ID No. 10 =  Sloning-REV GCCTTTGGGAAGCTTCTAAG SEQ ID No. 11 = POP2250 CGGCGGTTAGAACGCGGCTACAATTAATAC SEQ ID No. 12 = DigLigRev CATGATTACGCCAAGCTCAGAA SEQ ID No. 13 =  BC9 GTGACACGGCGGTTAGAACGCGGCTACAATTAATACATAACCCCATCCCCCTG TTGACAATTAATCATCGGCTCGTATAATGTGTGGAATTGTGAGCGGATAACAA TTTCACACAGGAAACAGGATCTACCATGCTGCCGGCGCCGAAAAACCTGGTTG TTTCTGAAGTTACCGAAGACTCTCTGCGTCTGTCTTGGNNNNNNNNNNNNNNN NNNNNNNNNNNNTTYGACTCTTTCCTGATCCAGTACCAGGAATCTGAAAAAGT TGGTGAAGCGATCAACCTGACCGTTCCGGGTTCTGAACGTTCTTACGACCTGA CCGGTCTGAAACCGGGTACCGAATACACCGTTTCTATCTACGGTGTTCTTAGA AGCTTCCCAAAGGC SEQ ID No. 14 = BC8 GTGACACGGCGGTTAGAACGCGGCTACAATTAATACATAACCCCATCCCCCTG TTGACAATTAATCATCGGCTCGTATAATGTGTGGAATTGTGAGCGGATAACAA TTTCACACAGGAAACAGGATCTACCATGCTGCCGGCGCCGAAAAACCTGGTTG TTTCTGAAGTTACCGAAGACTCTCTGCGTCTGTCTTGGNNNNNNNNNNNNNNN NNNNNNNNNTTYGACTCTTTCCTGATCCAGTACCAGGAATCTGAAAAAGTTGG TGAAGCGATCAACCTGACCGTTCCGGGTTCTGAACGTTCTTACGACCTGACCG GTCTGAAACCGGGTACCGAATACACCGTTTCTATCTACGGTGTTCTTAGAAGC TTCCCAAAGGC SEQ ID No. 15 = BC7 GTGACACGGCGGTTAGAACGCGGCTACAATTAATACATAACCCCATCCCCCTG TTGACAATTAATCATCGGCTCGTATAATGTGTGGAATTGTGAGCGGATAACAA TTTCACACAGGAAACAGGATCTACCATGCTGCCGGCGCCGAAAAACCTGGTTG TTTCTGAAGTTACCGAAGACTCTCTGCGTCTGTCTTGGNNNNNNNNNNNNNNN NNNNNNTTYGACTCTTTCCTGATCCAGTACCAGGAATCTGAAAAAGTTGGTGA AGCGATCAACCTGACCGTTCCGGGTTCTGAACGTTCTTACGACCTGACCGGTC TGAAACCGGGTACCGAATACACCGTTTCTATCTACGGTGTTCTTAGAAGCTTCC CAAAGGC SEQ ID No. 16 = BC6 GTGACACGGCGGTTAGAACGCGGCTACAATTAATACATAACCCCATCCCCCTG TTGACAATTAATCATCGGCTCGTATAATGTGTGGAATTGTGAGCGGATAACAA TTTCACACAGGAAACAGGATCTACCATGCTGCCGGCGCCGAAAAACCTGGTTG TTTCTGAAGTTACCGAAGACTCTCTGCGTCTGTCTTGGNNNNNNNNNNNNNNN NNNTTYGACTCTTTCCTGATCCAGTACCAGGAATCTGAAAAAGTTGGTGAAGC GATCAACCTGACCGTTCCGGGTTCTGAACGTTCTTACGACCTGACCGGTCTGA AACCGGGTACCGAATACACCGTTTCTATCTACGGTGTTCTTAGAAGCTTCCCA AAGGC SEQ ID No. 17 = 130 mer-L17A CGGCGGTTAGAACGCGGCTACAATTAATACATAACCCCATCCCCCTGTTGACA ATTAATCATCGGCTCGTATAATGTGTGGAATTGTGAGCGGATAACAATTTCAC ACAGGAAACAGGATCTACCATGCTG SEQ ID No. 18 = POP222ext CGG CGG TTA GAA CGC GGC TAC AAT TAA TAC SEQ ID No. 19 = LS1114 CCA AGA CAG ACG GGC AGA GTC TTC GGT AAC GCG AGA AAC AAC CAG GTT TTT CGG CGC CGG CAG CAT GGT AGA TCC TGT TTC SEQ ID No. 20 = LS1115 CCG AAG ACT CTG CCC GTC TGT CTT GG SEQ ID No. 21 = LS1117 CAG TGG TCT CAC GGA TTC CTG GTA CTG GAT CAG GAA AGA GTC GAA SEQ ID No. 22 = SDG10 CATGCGGTCTCTTCCGAAAAAGTTGGTGAAGCGATCGTCCTGACCGTTCCGGG T SEQ ID No. 23 = SDG24 GGTGGTGAAGATCGCAGACAGCGGGTTAG SEQ ID No. 24 = POP2222 CGGCGGTTAGAACGCGGCTAC SEQ ID No. 25 = SDG28 AAGATCAGTTGCGGCCGCTAGACTAGAACCGCTGCCACCGCCGGTGGTGAAG ATCGCAGAC SEQ ID No. 26 = FG12 GTGACACGGCGGTTAGAACGCGGCTACAATTAATACATAACCCCATCCCCCTG TTGACAATTAATCATCGGCTCGTATAATGTGTGGAATTGTGAGCGGATAACAA TTTCACACAGGAAACAGGATCTACCATGCTGCCGGCGCCGAAAAACCTGGTTG TTTCTCGCGTTACCGAAGACTCTGCGCGTCTGTCTTGGACCGCGCCGGACGCG GCGTTCGACTCTTTCCTGATCCAGTACCAGGAATCTGAAAAAGTTGGTGAAGC GATCGTGCTGACCGTTCCGGGTTCTGAACGTTCTTACGACCTGACCGGTCTGA AACCGGGTACCGAATACACCGTTTCTATCTACGGTGTTNNNNNNNNNNNNNNN NNNNNNNNNNNNNNNNNNNNNNNTCTAACCCGCTGTCTGCGATCTTCACCACC GGCGGTCACCATCACCATCACCATGGCAGCGGTTCTAGTCTAGCGGCCGCAAC TGATCTTGGC SEQ ID No. 27 = FG11 GTGACACGGCGGTTAGAACGCGGCTACAATTAATACATAACCCCATCCCCCTG TTGACAATTAATCATCGGCTCGTATAATGTGTGGAATTGTGAGCGGATAACAA TTTCACACAGGAAACAGGATCTACCATGCTGCCGGCGCCGAAAAACCTGGTTG TTTCTCGCGTTACCGAAGACTCTGCGCGTCTGTCTTGGACCGCGCCGGACGCG GCGTTCGACTCTTTCCTGATCCAGTACCAGGAATCTGAAAAAGTTGGTGAAGC GATCGTGCTGACCGTTCCGGGTTCTGAACGTTCTTACGACCTGACCGGTCTGA AACCGGGTACCGAATACACCGTTTCTATCTACGGTGTTNNNNNNNNNNNNNNN NNNNNNNNNNNNNNNNNNNNTCTAACCCGCTGTCTGCGATCTTCACCACCGGC GGTCACCATCACCATCACCATGGCAGCGGTTCTAGTCTAGCGGCCGCAACTGA TCTTGGC SEQ ID No. 28 = FG10 GTGACACGGCGGTTAGAACGCGGCTACAATTAATACATAACCCCATCCCCCTG TTGACAATTAATCATCGGCTCGTATAATGTGTGGAATTGTGAGCGGATAACAA TTTCACACAGGAAACAGGATCTACCATGCTGCCGGCGCCGAAAAACCTGGTTG TTTCTCGCGTTACCGAAGACTCTGCGCGTCTGTCTTGGACCGCGCCGGACGCG GCGTTCGACTCTTTCCTGATCCAGTACCAGGAATCTGAAAAAGTTGGTGAAGC GATCGTGCTGACCGTTCCGGGTTCTGAACGTTCTTACGACCTGACCGGTCTGA AACCGGGTACCGAATACACCGTTTCTATCTACGGTGTTNNNNNNNNNNNNNNN NNNNNNNNNNNNNNNNTCTAACCCGCTGTCTGCGATCTTCACCACCGGCGGTC ACCATCACCATCACCATGGCAGCGGTTCTAGTCTAGCGGCCGCAACTGATCTT GGC SEQ ID No. 29 = FG9 GTGACACGGCGGTTAGAACGCGGCTACAATTAATACATAACCCCATCCCCCTG TTGACAATTAATCATCGGCTCGTATAATGTGTGGAATTGTGAGCGGATAACAA TTTCACACAGGAAACAGGATCTACCATGCTGCCGGCGCCGAAAAACCTGGTTG TTTCTCGCGTTACCGAAGACTCTGCGCGTCTGTCTTGGACCGCGCCGGACGCG GCGTTCGACTCTTTCCTGATCCAGTACCAGGAATCTGAAAAAGTTGGTGAAGC GATCGTGCTGACCGTTCCGGGTTCTGAACGTTCTTACGACCTGACCGGTCTGA AACCGGGTACCGAATACACCGTTTCTATCTACGGTGTTNNNNNNNNNNNNNNN NNNNNNNNNNNNNTCTAACCCGCTGTCTGCGATCTTCACCACCGGCGGTCACC ATCACCATCACCATGGCAGCGGTTCTAGTCTAGCGGCCGCAACTGATCTTGGC SEQ ID No. 30 = FG8 GTGACACGGCGGTTAGAACGCGGCTACAATTAATACATAACCCCATCCCCCTG TTGACAATTAATCATCGGCTCGTATAATGTGTGGAATTGTGAGCGGATAACAA TTTCACACAGGAAACAGGATCTACCATGCTGCCGGCGCCGAAAAACCTGGTTG TTTCTCGCGTTACCGAAGACTCTGCGCGTCTGTCTTGGACCGCGCCGGACGCG GCGTTCGACTCTTTCCTGATCCAGTACCAGGAATCTGAAAAAGTTGGTGAAGC GATCGTGCTGACCGTTCCGGGTTCTGAACGTTCTTACGACCTGACCGGTCTGA AACCGGGTACCGAATACACCGTTTCTATCTACGGTGTTNNNNNNNNNNNNNNN NNNNNNNNNNTCTAACCCGCTGTCTGCGATCTTCACCACCGGCGGTCACCATC ACCATCACCATGGCAGCGGTTCTAGTCTAGCGGCCGCAACTGATCTTGGC SEQ ID No. 31 = FG7 GTGACACGGCGGTTAGAACGCGGCTACAATTAATACATAACCCCATCCCCCTG TTGACAATTAATCATCGGCTCGTATAATGTGTGGAATTGTGAGCGGATAACAA TTTCACACAGGAAACAGGATCTACCATGCTGCCGGCGCCGAAAAACCTGGTTG TTTCTCGCGTTACCGAAGACTCTGCGCGTCTGTCTTGGACCGCGCCGGACGCG GCGTTCGACTCTTTCCTGATCCAGTACCAGGAATCTGAAAAAGTTGGTGAAGC GATCGTGCTGACCGTTCCGGGTTCTGAACGTTCTTACGACCTGACCGGTCTGA AACCGGGTACCGAATACACCGTTTCTATCTACGGTGTTNNNNNNNNNNNNNNN NNNNNNNTCTAACCCGCTGTCTGCGATCTTCACCACCGGCGGTCACCATCACC ATCACCATGGCAGCGGTTCTAGTCTAGCGGCCGCAACTGATCTTGGC SEQ ID NO: 32 = human mature PD-L1 FTVTVPKDLYVVEYGSNMTIECKFPVEKQLDLAALIVYWEMEDKNIIQFVHGEED LKVQHSSYRQRARLLKDQLSLGNAALQITDVKLQDAGVYRCMISYGGADYKRIT VKVNAPYNKINQRILVVDPVTSEHELTCQAEGYPKAEVIWTSSDHQVLSGKTTTT NSKREEKLFNVTSTLRINTTTNEIFYCTFRRLDPEENHTAELVIPELPLAHPPNER SEQ ID NO: 33 = human mature PD-1 PGWFLDSPDRPWNPPTFSPALLVVTEGDNATFTCSFSNTSESFVLNWYRMSPSNQT DKLAAFPEDRSQPGQDCRFRVTQLPNGRDFHMSVVRARRNDSGTYLCGAISLAPK AQIKESLRAELRVTERRAEVPTAHPSPSPRPAGQFQTLVVGVVGGLLGSLVLLVW VLAVICSRAARGTIGARRTGQPLKEDPSAVPVFSVDYGELDFQWREKTPEPPVPCV PEQTEYATIVFPSGMGTSSPARRGSADGPRSAQPLRPEDGHCSWPL SEQ Clone ID NO: AA Sequence ISOP121HR5P1G9 34 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFPINYGERATKGE AINLYVPGSERSYDLTGLKPGTEYWVLIGGVKGGLKSSPLWAW FTT ISOP121BR5P1F7 35 LPAPKNLVVSRVTEDSARLSWHDATWQYFDSFLIQYQESEKVG EAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVFHRKHIDFVSNPLS AIFTT ISOP121BR5P1A6 36 LPAPKNLVVSRVTEDSARLSWASWLVAFFDSFLIQYQESEKVG EAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYQRHASAFVSNPL SAIFTT ISOP121BR5P1C5 37 LPAPKNLVVSRVTEDSARLSWFRLRIVQTFDSFLIQYQESEKVG EAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVITVVELLQQSNPLS AIFTT ISOP121BR5P1D7 38 LPAPKNLGCFSRYRRLSRLSWETPYPSLSNFDSFLIQYQESEKVG EAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVLKLSAAWWPSNP LSAIFTT ISOP121BR5P1C6 39 LPAPKNLVVSRVTEDSARLSWRKQEQYFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYSRPKAEFTSNPLSA IFTT ISOP121AR5P1G6 40 LPAPKNLVVSRVTEDSARLSWHATFGDPFDSFLIQYQESEKVG EAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVGRHYTVYDSNPLS AIFTT ISOP121BR5P1B7 41 LPAPKNLVVSRITEDSARLSWKWEEGFFDSFLIQYQESEKVGEA IVLTVPGSERSYDLTGLKPGTEYTVSIYGVYQRHASAFVSNPLSA IFTT ISOP121FR5P1G1 42 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFWIHYTEAPVHGE AIVLTVPGSERSYDLTGLKPGTEYTVVIWGVKGGTWSSPLSAIF TT ISOP121GR5P1B4 43 LPAPKNLIVSRVTEDSARLSWTAPDAAFDSFPINYGERATKGEA INLYVPGSERSYDLTGLKPGTEYWVLIGGVKGGLKSSPLWAWF TT ISOP121BR5P1G2 44 LPAPKNLVVSRVTEDSARLSWADELHHANHFDSFLIQYQESEK VGEAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYDRHYEIHFYS NPLSAIFTT ISOP121HR5P1H2 45 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFDIYYLEYDYSGEA IVLTVPGSERSYDLTGLKPGTEYDVLIIGVKGGSLSTPLSAIFTT ISOP121FR5P1G11 46 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFSIWYLEIVAHGE AIVLTVPGSERSYDLTGLKPGTEYEVIIHGVKGCGPSGPLSAIFTT ISOP121AR5P1E7 47 LPAPKNLVVSRVTEDSARLSWHVYHEIDYFDSFLIQYQESEKVG EAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYQRKVEFYSNPLS AIFTT ISOP121GR5P1F6 48 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFDIRYHEYTWPGE AIVLLVPGSERSYDLTGLKPGTEYGVYINGVKGGFRSKPLFAWF TTGG ISOP121BR5P1E9 49 LPAPKNLVVSRVTEDSARLSWDSYRDYFDSFLIQYQESEKVGEA IVLTVPGSERSYDLTGLKPGTEYTVSIYGVYSRKHVVFVQSNPLS AIFTT ISOP121AR5P1F2 50 LPAPKNLVISRVTEDSARLSWGWSELIATHFDSFLIQYQESEKV GEAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYNRKVNFYSNPL SAIFTT ISOP121AR5P1F7 51 LPAPKNLVVSRVTEDSARLSWQEHWDTSSNFDSFLIQYQESEK VGEAIVLTVPGSERSYDLTGLKPGTEYTISIYGVYNRKVLFYSNPL SAIFTT ISOP121BR5P1H6 52 LPAPKNLVVSRVTEDSARLSWGYIDVSYFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYSRPKAEFTSNPLSA IFTT ISOP121GR5P1A2 53 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFKIQYIERYIPGEAI QLNVPGSERSYDLTGLKPGTEYSVIIPGVKGGRNSFPLWAWFT T ISOP121BR5P1D3 54 LPAPKNLVVSRVTEDSARLSWYEDNTERFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYIRVQVLWFSNPLS AIFTT ISOP121AR5P1F9 55 LPAPKNLVVSRVTEDSARLSWGWSELIATHFDSFLIQYQESEKV GEAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYNRKVNFYSNPL SAIFTT ISOP121AR5P1H5 56 LPAPKNLVVSRVTEDSARLSWEDAVKHIWFDSFLIQYQESEKV GEAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVWIASVWRSNPL SAIFTT ISOP121AR5P1G10 57 LPAPKNLVVSRVTEDSARLSWEWLEHFDSFLIQYQESEKVGEAI VLTVPGSERSYDLTGLKPGTEYTVSIYGVYQRKVEFHSNPLSAIF TTT ISOP121AR5P1F3 58 LPAPKNLVVSRVTEDSARLSWPFNNYSEHFDSFLIQYQESEKVG EAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYERKTAFYSNPLSA IFTT ISOP121BR5P1E2 59 LPAPKNLVVSRVTEDSARLSWWFPLEWFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYTREHKSVWASNP LSAIFTT ISOP121BR5P1D1 60 LPAPKNLVVSRVTEDSARLSWKWGGEFFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYQRNWHHWYSNP LSAIFTT ISOP121BR5P1C9 61 LPAPKNLVVSRVTEDSARLSWIWPDKHEFFDSFLIQYQESEKVG EAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYDRKYANWSSNP LSAIFTT ISOP121GR5P1G11 62 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFQINYHEYGQNG EAIQLIVPGSERSYDLTGLKPGTEYGVWIWGVKGGIRSKPLWA FFTT ISOP121BR5P1A7 63 LPAPKNLVVSRVTEDSARLSWTTAFHNEYFDSFLIQYQESEKVG EAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYSRPKAEFTSNPLS AIFTT ISOP121BR5P1C3 64 LPAPKNLVVSRVTEDSARLSWASARDYFDSFLIQYQESEKVGEA IVLTVPGSERSYDLTGLKPGTEYTVSIYGVLAIAQITHWFSNPLS AIFTT ISOP121AR5P1D11 65 LPAPKNLVVSRVTEDSARLSWEWLEHFDSFLIQYQESEKVGEAI VLTVPGSERSYDLTGLKPGTEYTVSIYGVYQRKVEFHSNPLSAIF TT ISOP121ER5P1E7 66 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFTIGYTETPPRGEA IVLTVPGSERSYDLTGLKPGTKYYVSILGVKGGLGSWPLSAIFTT ISOP121GR5P1G7 67 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFHIRYHEYDKNGE AIQLYVPGSERSYDLTGLKPGTEYGVYIHGVKGGGRSKPLWAH FTT ISOP121AR5P1A8 68 LPAPKNLVVSRVTEDSARLSWGLEWAYQFFDSFLIQYQESEKV GEAIVLTVPGSERSYDLTGLKPGTEYIVSIYGVYLRAIEFYSNPLS AIFTT ISOP121BR5P1E7 69 LPAPKNLVVSRVTEDSARLSWRKQEQYFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVKKWPSTTTTSNPLS AIFTT ISOP121FR5P1H8 70 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFVIYYSEQHFYGE AIVLTVPGSERSYDLTGLKPGTEYVVKIYGVKGGETSKPLSAIFTT ISOP121GR5P1D2 71 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFHILYQERAQSGE AIGLVVPGSERSYDLTGLKPATEYSVQIFGVKGGKLSNPLWAW FTT ISOP121AR5P1H2 72 LPAPKNLVVSRVTEDSARLSWVIDEFIPLFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVLAKNIGISNPLSAIFT T ISOP121GR5P1F10 73 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFFIDYVERATVGE AIALNVPGSKRSYALTGLKPGTEYFVKIRGVKGGLKSKPLWAW FTT ISOP121BR5P1A2 74 LPAPKNLVVSRVTEDSARLSWRFSQEWFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYARGIHKWLSNPLS AIFTT ISOP121GR5P1F7 75 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFGINYVERASEGE AIDLGVPGSERSYDLTGLKPGTEYFVKIFGVKGGIPSVPLWAWF TT ISOP121AR5P1B8 76 LPAPKNLVISRVTEDSARLSWDKRTQFAFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVPTWSGRTQSNPLS AIFTT ISOP121GR5P1D7 77 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFKIWYQERSIVGE AIFLLVPGSERSYDLTGLKPGTEYIVQIFGVKGGPYSNPLWAPFT T ISOP121BR5P1G3 78 LPAPKNLVVSRVTEDSARLSWKQRTSFHFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVPFWQQWQPESNP LSAIFTT ISOP121AR5P1C5 79 LPAPKNLVVSRVTEDSARLSWKRSDDEWFDSFLIQYQESEKVG EAIILTVPGSERSYDLTGLKPGTEYTVSIYGVYQRAALWFSNPLS AIFTT ISOP121FR5P1H9 80 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFSILYGETAPIGEAI VLTVPGSERSYDLTGLKPGTEYVVYIQGVKGGNYSQPLSAIFTT ISOP121AR5P1A10 81 LPAPKNLVVSRVTEDSARLSWPDWSNSEYFDSFLIQYQESEKV GEAIVLTVPGSERSYDLTGLKPGTEYIVSIYGVYARHRLFVSNPL SAIFTT ISOP121HR5P1F2 82 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFTILYGETYSGGEA IVLTVPGSERSYDLTGLKPGTEYVVYIFGVKGGKWSRPLSAIFTT ISOP121AR5P1H1 83 LPAPKNLVVSRVTEDSARLSWKQATKFVFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVPDWFVLESNPLSAI FTT ISOP121BR5P1D10 84 LPAPKNLVVSRVTEDSARLSWGKKSHFFDSFLIQYQESEKVGEA IVLTVPGSERSYDLTGLKPGTEYTVSIYGVYTRGQCEWESNQLS AIFFTT ISOP121BR5P1F10 85 LPAPKNLVVSRVTEDSARLSWPLNLEYFDSFLIQYQESEKVGEAI VLTVPGSERSYDLTGLKPGTEYTVSIYGVYGRYGGPFVSNPLSAI FTT ISOP121BR5P1D11 86 LPAPKNLVVSRVTEDSARLSWFNADEEYFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYVRAVRFVSSNPLS AIFTT ISOP121AR5P1E11 87 LPAPKNLVVSRVTEDSARLSWSVQTSFVFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVPLWHGFDSNPLSAI FTT ISOP121BR5P1D6 88 LPAPKNLVVSRVTEDSARLSWKQGTSFHFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVQLLANDIISSNPLSAI FTT ISOP121BR5P1B5 89 LPAPKNLVVSRVTEDSARLSWRKQEQYFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYQRGYHNWFSNPL SAIFTT ISOP194ER9P1G3 90 LPAPKNLIVSRVTEDSARLSWTAPDAAFDSFRIAYYETMVSGEA IVLTVPGSERSYDLTGLKPGTEYAVIIKGVKGGKPSWPLSAIFTT ISOP194AR9P1F2 91 LPAPKNLVISRVTEDSARLSWEWLEHFDSFLIQYQESEKVGEAI VLTVPGSERSYDLTGLKPGTEYTVSIYGVYNRKVNFYSNPLSAIF TT ISOP194AR9P1H10 92 LPAPKNLVISRVTEDSARLSWPAHYHSAFFDSFLIQYQESEKVG EAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYQRKVEFHSNPLS AIFTT ISOP194BR9P1H4 93 LPAPKNLVVSRVTEDSACLSWTTAFHNEYFDSFLIQYQESEKVG EAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYSRPKAEFTSNPLS AIFTT ISOP194AR9P1D8 94 LPAPKNLVVSRVTEDSARLSWDTWNDFFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYQRKVIWLSNPLSA IFTT ISOP194BR9P1D1 95 LPAPKNLVVSRVTEDSARLSWEHSLLNDQWFDSFLIQYQESEK VGEAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYQRGRALWYS NPLSAIFTT ISOP194AR9P1E8 96 LPAPKNLVVSRVTEDSARLSWEWLEHFDSFLIQYQESEKVGEAI VLTIPGSERSYDLTGLKPGTEYTVSIYGVYQRKVEFHSNPLSAIFT T ISOP194AR9P1E9 97 LPAPKNLVVSRVTEDSARLSWEWLEHFDSFLIQYQESEKVGEAI VLTVPGSERSYDLTGLKPGTEYTVSIYGVYQRKVNFYSNPLSAIF TT ISOP194AR9P1H9 98 LPAPKNLVVSRVTEDSARLSWEWLEHFDSFQIQYQESEKVGEA IVLTVPGSERSYDLTGLKPGTEYIVSIYGVYQRKVEFHSNPLSAIF TT ISOP194BR9P1A9 99 LPAPKNLVVSRVTEDSARLSWFNADEEYFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYDRKVKFVQSNPLS AIFTT ISOP194BR9P1A5 100 LPAPKNLVVSRVTEDSARLSWFNADEEYFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYQRGYHNWFSNPL SAIFTT ISOP194BR9P1F7 101 LPAPKNLVVSRVTEDSARLSWFNADEEYFDSFLIQYQESEKVGE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYTRGRYEWRESNPL SAIFTT ISOP194AR9P1G7 102 LPAPKNLVVSRVTEDSARLSWGDDFNSEYFDSFLIQYQESEKV GEAIVLTVPGSERSYDLTGLKPGTEYIVSIYGVYTRAVVFTSNPL SAIFTT ISOP194AR9P1E3 103 LPAPKNLVVSRVTEDSARLSWKRSDDEWFDSFLIQYQESEKVG EAIVLTVPGSERSYDLTGLKPGTEYIVSIYGVYQRAALWFSNPLS AIFTT ISOP194AR9P1C5 104 LPAPKNLVVSRVTEDSARLSWLRDFNGRAFFDSFLIQYQESEKV GEAIVLTVPGSERSYDPTGLKPGTEYIVSIYGVFITWIHVRSNPL SAIFTT ISOP194AR9P1H3 105 LPAPKNLVVSRVTEDSARLSWNASWISHNFFDSFLIQYQESEK VGEAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYERKTAFYSNP LSAIFTT ISOP194GR9P1E9 106 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFHIRYHEYDKNGE AIQLYVPGSERSYDLTGLKPGTEYGVFIWGVKGGLKSKPLWAW FTT ISOP194HR9P1B10 107 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFPIRYYERANGEAI VLTVPGSERSYDLTGLKPGTEYIVWIYGVKGGGRSGPLSAIFTT ISOP194ER9P1A11 108 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFRIAYYETMVSGE AIVLTVPGSERSYDLTGLKPGTEYAVIIKGVKGGKPSWPLSAIFT T ISOP194ER9P1A3 109 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFRIAYYETMVSGE AIVLTVPGSERSYDLTGLKPGTEYAVIIKGVKGGMVSWPLSAIFT T ISOP194ER9P1H9 110 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFRIAYYETMVSGE AIVLTVPGSERSYDLTGPKPGTEYAVIIKGVKGGKPSWPLSAIFT T ISOP194HR9P1B2 111 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFSILYGELIGDGEAI VLTVPGSERSYDLTGLKPGSEYTVYIFGVKGGRYSRPLSAIFTT ISOP194HR9P1D11 112 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFSILYGELIGDGEAI VLTVPGSERSYDLTGLKPGTEYTVYIFGVKGGRYSRPLSAIFTT ISOP194GR9P1F6 113 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFWIDYWERLSEGE AIALRVPGSERSYDLTGLKPGTEYYVWIVGVKGGKFSQPLRAW FTT ISOP194GR9P1F9 114 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFWIFYNERWQNG EAIRLIVPGSERSYDLTGLKPGTEYSVIIPGVKGGRNSFPLWAWF TT ISOP194GR9P1C11 115 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFWIFYNERWQNG EAIRLTVPGSERSYDLTGLKPGTEYWVLIGGVKGGLKSSPLWA WFTT ISOP194ER9P1E6 116 LPAPKNLVVSRVTEDSARLSWTAPDAAFDSFWIKYYEKRNPGE AIVLTVPGSERSYDLTGLKPGTEYLVIISGVKGGSRSVPLSAIFTT ISOP194BR9P1G9 117 LPAPKNLVVSRVTEDSARLSWTTAFHNEYFDSFLIQYQESEKVG EAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYIRVQVLWFSNPL SAIFTT ISOP194BR9P1E4 118 LPAPKNLVVSRVTEDSARLSWTTAFHNEYFDSFLIQYQESEKVG EAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYQRGYHNWFSNP LSAIFTT ISOP194AR9P1H1 119 LPAPKNLVVSRVTEDSARLSWWRVLGHSHFFDSFLIQYQESEK VGEAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYNRKVNFYSNP LSAIFTT ISOP194BR9P1D10 120 LPAPKNLVVSRVTEDSARLSWYEDNTERFDSFLIQYQESEKVVE AIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYIRVQVLWFSNPLS AIFTT ISOP194BR9P1C8 121 LPAPKNLVVSRVTEDSARLSWYFAGELWFDSFLIQYQESEKVG EAIVLTVPGSERSYDLTGLKPGTEYTVSIYGVYQRGYHNWFSNP LSAIFTT ISOP194AR9P1C10 122 LPAPKNLVVSRVTEDSARPSWEWLEHFDSFLIQYQESEKVGEAI VLTVPGSERSYDLTGLKPGTEYTVSIYGVYNRKVNFYSNPLSAIF TT ISOP194AR9P1D11 123 LPAPKNLVVSRVTEDSGRLSWQHHISFFDSFLIQYQESEKVGEA IVLTVPGSERSYDLTGLKPGTEYTVSIYGVYNRKVNFYSNPLSAIF TT ISOP194AR9P1C3 124 LPAPKNLVVSRVTQNSARLSWEWLEHFDSFLIHYQESEKVGEA IVLTVPGSERSYDLTGLKPGTEYTVSIYGVYQRKVEFHSNPLSAIF TT 3rd FN3 domain of 125 DAPSQIEVKDVTDTTALITWFKPLAEIDGIELTYGIKDVP tenascin C (TN3 GDRTTIDLTEDENQYSIGNLKPDTEYEVSLISRR GDMSSNPAKETFTT Fibcon 126 LDAPTDLQVTNVTDTSITVSWTPPSATITGYRITYTPSNG PGEPKELTVPPSSTSVTITGLTPGVEYVVSLYAL KDNQESPPLVGTQTT 10^(th) FN3 domain of 127 VSDVPRDLEVVAATPTSLLISWDAPAVTVRYYRITYGET fibronectin GGNSPVQEFTVPGSKSTATISGLKPGVDYTITVY AVTGRGDSPASSKPISINYRT Linker 128 GSGS Linker 129 GGGSGGGS Linker 130 GGGGSGGGGSGGGGSGGGGSGGGGS Linker 131 APAP Linker 132 APAPAPAPAP Linker 133 APAPAPAPAPAPAPAPAPAP Linker 134 APAPAPAPAPAPAPAPAPAPAPAPAPAPAPAPAPAPAPAP Linker 135 EAAAKEAAAKEAAAKEAAAKEAAAKAAA Albumin variant 136 DAHKSEVAHRFKDLGEENFKALVLIAFAQYLQQSPFED HVKLVNEVTEFAKTCVADESAENCDKSLHTLFG DKLCTVATLRETYGEMADCCAKQEPERNECFL QHKDDNPNLPRLVRPEVDVMCTAFFIDNEETFL KKYLYEIARRHPYFYAPELLFFAKRYKAAFTEC CQAADKAACLLPKLDELRDEGKASSAKQRLKC ASLQKFGERAFKAWAVARLSQRFPKAEFAEVSK LVTDLTKVHTECCHGDLLECADDRADLAKYICE NQDSISSKLKECCEKPLLEKSHCIAEVENDEMPA DLPSLAADFVESKDVCKNYAEAKDVFLGMFLY EYARRHPDYSVVLLLRLAKTYETTLEKCCAAAD PHECYAKVFDEFKPLVEEPQNLIKQNCELFEQLG EYKFQNALLVRYTKKVPQVSTPTLVEVSRNLGK VGSKCCKHPEAKRMPCAEDYLSVVLNQLCVLH EKTPVSDRVTKCCTESLVNRRPCFSALEVDETY VPKEFNAETFTFHADICTLSEKERQIKKQTALVE LVKHKPKATKEQLKAVMDDFAAFVEKCCKAD DKETCFAEEGKKLVAASQAALGL 

What is claimed:
 1. A protein comprising an amino acid sequence that is at least 95% identical to a sequence selected from the group consisting of SEQ ID NOs: 34, 35, 36, 37, 38, 39, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, and
 124. 2. The protein of claim 1, wherein the protein has at least one substitution at a residue selected from the group consisting of 11, 14, 17, 37, 46, 73, and 86 corresponding to SEQ ID NO:
 4. 3. The protein of claim 1, wherein the protein is conjugated to a heterologous molecule.
 4. The protein of claim 3, wherein the heterologous molecule is a detectable label, a cytotoxic agent, or both.
 5. The protein of claim 4, wherein the detectable label is selected from a radioactive isotope, a magnetic bead, a metallic bead, a colloidal particle, a fluorescent dye, an electron-dense reagent, an enzyme, a biotin, a digoxigenin, a hapten, a luminescent molecule, a chemiluminescent molecule, a fluorochrome, a fluorophore, a fluorescent quenching agent, a colored molecule, a scintillant, an avidin, a streptavidin, a protein A, a protein G, an antibody, an antibody fragment, a polyhistidine, a Ni²⁺, a flag tag, a myc tag, a heavy metal, an alkaline phosphatase, a peroxidase, a luciferase, an electron donor, an electron acceptor, an acridinium ester, or a colorimetric substrate.
 6. The protein of claim 4, wherein the detectable label is auristatin, monomethyl auristatin phenylalanine, dolostatin, chemotherapeutic agent, a drug, a growth inhibitory agent, a toxin, or a radioactive isotope.
 7. The protein of claim 4, wherein the detectable label is conjugated to the protein by a linker.
 8. The protein of claim 4, wherein the detectable label is complexed with a chelating agent.
 9. The protein of claim 1, further comprising a methionine at the N-terminus of the protein.
 10. The protein of claim 1, wherein the protein is coupled to a half-life extending moiety.
 11. The protein of claim 10, wherein the half-life extending moiety is an albumin binding molecule, a polyethylene glycol (PEG), albumin, albumin variant, or at least a portion of an Fc region of an immunoglobulin.
 12. A composition comprising the protein of claim 1 and a pharmaceutically acceptable carrier.
 13. A kit comprising the protein of claim
 1. 